Hello.
The build (actually, linking) failure described in [1] affects current
stable (6.13.4). Could the commit that fixes it in mainline, namely,
c40ca9ef7c5c9bbb0d2f7774c87417cc4f1713bf ("drm: select DRM_KMS_HELPER
from DRM_GEM_SHMEM_HELPER") be backported to 6.13.x, please?
Thank you.
[1]
https://lore.kernel.org/all/20250121-greedy-flounder-of-abundance-4d2ee8-mk…
The patch titled
Subject: mm: abort vma_modify() on merge out of memory failure
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-abort-vma_modify-on-merge-out-of-memory-failure.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patche…
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com>
Subject: mm: abort vma_modify() on merge out of memory failure
Date: Sat, 22 Feb 2025 16:19:52 +0000
The remainder of vma_modify() relies upon the vmg state remaining pristine
after a merge attempt.
Usually this is the case, however in the one edge case scenario of a merge
attempt failing not due to the specified range being unmergeable, but
rather due to an out of memory error arising when attempting to commit the
merge, this assumption becomes untrue.
This results in vmg->start, end being modified, and thus the proceeding
attempts to split the VMA will be done with invalid start/end values.
Thankfully, it is likely practically impossible for us to hit this in
reality, as it would require a maple tree node pre-allocation failure that
would likely never happen due to it being 'too small to fail', i.e. the
kernel would simply keep retrying reclaim until it succeeded.
However, this scenario remains theoretically possible, and what we are
doing here is wrong so we must correct it.
The safest option is, when this scenario occurs, to simply give up the
operation. If we cannot allocate memory to merge, then we cannot allocate
memory to split either (perhaps moreso!).
Any scenario where this would be happening would be under very extreme
(likely fatal) memory pressure, so it's best we give up early.
So there is no doubt it is appropriate to simply bail out in this
scenario.
However, in general we must if at all possible never assume VMG state is
stable after a merge attempt, since merge operations update VMG fields.
As a result, additionally also make this clear by storing start, end in
local variables.
The issue was reported originally by syzkaller, and by Brad Spengler (via
an off-list discussion), and in both instances it manifested as a
triggering of the assert:
VM_WARN_ON_VMG(start >= end, vmg);
In vma_merge_existing_range().
It seems at least one scenario in which this is occurring is one in which
the merge being attempted is due to an madvise() across multiple VMAs
which looks like this:
start end
|<------>|
|----------|------|
| vma | next |
|----------|------|
When madvise_walk_vmas() is invoked, we first find vma in the above
(determining prev to be equal to vma as we are offset into vma), and then
enter the loop.
We determine the end of vma that forms part of the range we are
madvise()'ing by setting 'tmp' to this value:
/* Here vma->vm_start <= start < (end|vma->vm_end) */
tmp = vma->vm_end;
We then invoke the madvise() operation via visit(), letting prev get
updated to point to vma as part of the operation:
/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
error = visit(vma, &prev, start, tmp, arg);
Where the visit() function pointer in this instance is
madvise_vma_behavior().
As observed in syzkaller reports, it is ultimately madvise_update_vma()
that is invoked, calling vma_modify_flags_name() and vma_modify() in turn.
Then, in vma_modify(), we attempt the merge:
merged = vma_merge_existing_range(vmg);
if (merged)
return merged;
We invoke this with vmg->start, end set to start, tmp as such:
start tmp
|<--->|
|----------|------|
| vma | next |
|----------|------|
We find ourselves in the merge right scenario, but the one in which we
cannot remove the middle (we are offset into vma).
Here we have a special case where vmg->start, end get set to perhaps
unintuitive values - we intended to shrink the middle VMA and expand the
next.
This means vmg->start, end are set to... vma->vm_start, start.
Now the commit_merge() fails, and vmg->start, end are left like this.
This means we return to the rest of vma_modify() with vmg->start, end
(here denoted as start', end') set as:
start' end'
|<-->|
|----------|------|
| vma | next |
|----------|------|
So we now erroneously try to split accordingly. This is where the
unfortunate stuff begins.
We start with:
/* Split any preceding portion of the VMA. */
if (vma->vm_start < vmg->start) {
...
}
This doesn't trigger as we are no longer offset into vma at the start.
But then we invoke:
/* Split any trailing portion of the VMA. */
if (vma->vm_end > vmg->end) {
...
}
Which does get invoked. This leaves us with:
start' end'
|<-->|
|----|-----|------|
| vma| new | next |
|----|-----|------|
We then return ultimately to madvise_walk_vmas(). Here 'new' is unknown,
and putting back the values known in this function we are faced with:
start tmp end
| | |
|----|-----|------|
| vma| new | next |
|----|-----|------|
prev
Then:
start = tmp;
So:
start end
| |
|----|-----|------|
| vma| new | next |
|----|-----|------|
prev
The following code does not cause anything to happen:
if (prev && start < prev->vm_end)
start = prev->vm_end;
if (start >= end)
break;
And then we invoke:
if (prev)
vma = find_vma(mm, prev->vm_end);
Which is where a problem occurs - we don't know about 'new' so we
essentially look for the vma after prev, which is new, whereas we actually
intended to discover next!
So we end up with:
start end
| |
|----|-----|------|
|prev| vma | next |
|----|-----|------|
And we have successfully bypassed all of the checks madvise_walk_vmas()
has to ensure early exit should we end up moving out of range.
We loop around, and hit:
/* Here vma->vm_start <= start < (end|vma->vm_end) */
tmp = vma->vm_end;
Oh dear. Now we have:
tmp
start end
| |
|----|-----|------|
|prev| vma | next |
|----|-----|------|
We then invoke:
/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
error = visit(vma, &prev, start, tmp, arg);
Where start == tmp. That is, a zero range. This is not good.
We invoke visit() which is madvise_vma_behavior() which does not check the
range (for good reason, it assumes all checks have been done before it was
called), which in turn finally calls madvise_update_vma().
The madvise_update_vma() function calls vma_modify_flags_name() in turn,
which ultimately invokes vma_modify() with... start == end.
vma_modify() calls vma_merge_existing_range() and finally we hit:
VM_WARN_ON_VMG(start >= end, vmg);
Which triggers, as start == end.
While it might be useful to add some CONFIG_DEBUG_VM asserts in these
instances to catch this kind of error, since we have just eliminated any
possibility of that happening, we will add such asserts separately as to
reduce churn and aid backporting.
Link: https://lkml.kernel.org/r/20250222161952.41957-1-lorenzo.stoakes@oracle.com
Fixes: 2f1c6611b0a8 ("mm: introduce vma_merge_struct and abstract vma_merge(),vma_modify()")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com>
Tested-by: Brad Spengler <brad.spengler(a)opensrcsec.com>
Reported-by: Brad Spengler <brad.spengler(a)opensrcsec.com>
Reported-by: syzbot+46423ed8fa1f1148c6e4(a)syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-mm/6774c98f.050a0220.25abdd.0991.GAE@google.c…
Cc: Jann Horn <jannh(a)google.com>
Cc: Liam Howlett <liam.howlett(a)oracle.com>
Cc: Vlastimil Babka <vbabka(a)suse.cz>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
mm/vma.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
--- a/mm/vma.c~mm-abort-vma_modify-on-merge-out-of-memory-failure
+++ a/mm/vma.c
@@ -1509,24 +1509,28 @@ int do_vmi_munmap(struct vma_iterator *v
static struct vm_area_struct *vma_modify(struct vma_merge_struct *vmg)
{
struct vm_area_struct *vma = vmg->vma;
+ unsigned long start = vmg->start;
+ unsigned long end = vmg->end;
struct vm_area_struct *merged;
/* First, try to merge. */
merged = vma_merge_existing_range(vmg);
if (merged)
return merged;
+ if (vmg_nomem(vmg))
+ return ERR_PTR(-ENOMEM);
/* Split any preceding portion of the VMA. */
- if (vma->vm_start < vmg->start) {
- int err = split_vma(vmg->vmi, vma, vmg->start, 1);
+ if (vma->vm_start < start) {
+ int err = split_vma(vmg->vmi, vma, start, 1);
if (err)
return ERR_PTR(err);
}
/* Split any trailing portion of the VMA. */
- if (vma->vm_end > vmg->end) {
- int err = split_vma(vmg->vmi, vma, vmg->end, 0);
+ if (vma->vm_end > end) {
+ int err = split_vma(vmg->vmi, vma, end, 0);
if (err)
return ERR_PTR(err);
_
Patches currently in -mm which might be from lorenzo.stoakes(a)oracle.com are
mm-abort-vma_modify-on-merge-out-of-memory-failure.patch
mm-simplify-vma-merge-structure-and-expand-comments.patch
mm-further-refactor-commit_merge.patch
mm-eliminate-adj_start-parameter-from-commit_merge.patch
mm-make-vmg-target-consistent-and-further-simplify-commit_merge.patch
mm-completely-abstract-unnecessary-adj_start-calculation.patch
mm-madvise-split-out-mmap-locking-operations-for-madvise-fix.patch
mm-use-read-write_once-for-vma-vm_flags-on-migrate-mprotect.patch
mm-refactor-rmap_walk_file-to-separate-out-traversal-logic.patch
mm-provide-mapping_wrprotect_range-function.patch
fb_defio-do-not-use-deprecated-page-mapping-index-fields.patch
fb_defio-do-not-use-deprecated-page-mapping-index-fields-fix.patch
mm-allow-guard-regions-in-file-backed-and-read-only-mappings.patch
selftests-mm-rename-guard-pages-to-guard-regions.patch
tools-selftests-expand-all-guard-region-tests-to-file-backed.patch
tools-selftests-add-file-shmem-backed-mapping-guard-region-tests.patch
This is based on top of
https://git.kernel.org/pub/scm/linux/kernel/git/mmind/linux-rockchip.git/lo…
6ee0b9ad3995 ("arm64: dts: rockchip: Add rng node to RK3588") as it
depends on the (merged) series from
https://lore.kernel.org/all/20250211-pre-ict-jaguar-v6-0-4484b0f88cfc@cherr…
Patches for Haikou Video Demo adapter for PX30 Ringneck and RK3399 Puma
(patches 4 and 5) also depend on the following patch series:
https://lore.kernel.org/linux-devicetree/20250220-pca976x-reset-driver-v1-0…
This fixes incorrect pinmux on UART0 and UART5 for PX30 Ringneck on
Haikou.
This adds support for the HAIKOU-LVDS-9904379 adapter for PX30 Ringneck
fitted on a Haikou carrierboard.
Additionally, this adds support for Haikou Video Demo adapter on PX30
Ringneck and RK3399 Puma fitted on a Haikou carrierboard. Notably
missing from the overlay is the OV5675 camera module which expects
19.2MHz which we cannot exactly feed right now. Modifications to the
OV5675 drivers will be made so it's more flexible and then support for
the camera module will be added. This adapter has a 720x1280 DSI display
with a GT911 touchscreen, a GPIO-controllable LED and an I2C GPIO
expander. Support for this adapter on RK3588 Tiger is being added in a
separate patch series[1].
Note that the DSI panel currently is glitchy on both PX30 Ringneck and
RK3399 Puma but this is being tackled in another series[2]. Since this
will not be fixed through DT properties for the panel, adding the DT
nodes for the DSI panel even if not perfect right now seems acceptable
to me.
[1] https://lore.kernel.org/linux-rockchip/20241127143719.660658-1-heiko@sntech…
[2] https://lore.kernel.org/r/20240626084722.832763-1-heiko@sntech.de
Signed-off-by: Quentin Schulz <quentin.schulz(a)cherry.de>
---
Changes in v2:
- rename uart5_rts_gpio to uart5_rts_pin to stop triggering a false
positive of the dtschema checker,
- remove PU from uart5_rts_pin,
- Link to v1: https://lore.kernel.org/r/20250220-ringneck-dtbos-v1-0-25c97f2385e6@cherry.…
---
Quentin Schulz (5):
arm64: dts: rockchip: fix pinmux of UART0 for PX30 Ringneck on Haikou
arm64: dts: rockchip: fix pinmux of UART5 for PX30 Ringneck on Haikou
arm64: dts: rockchip: add support for HAIKOU-LVDS-9904379 adapter for PX30 Ringneck
arm64: dts: rockchip: add overlay for PX30 Ringneck Haikou Video Demo adapter
arm64: dts: rockchip: add overlay for RK3399 Puma Haikou Video Demo adapter
arch/arm64/boot/dts/rockchip/Makefile | 15 ++
.../px30-ringneck-haikou-lvds-9904379.dtso | 130 ++++++++++++++
.../rockchip/px30-ringneck-haikou-video-demo.dtso | 190 +++++++++++++++++++++
.../boot/dts/rockchip/px30-ringneck-haikou.dts | 10 +-
.../rockchip/rk3399-puma-haikou-video-demo.dtso | 166 ++++++++++++++++++
5 files changed, 510 insertions(+), 1 deletion(-)
---
base-commit: 6ee0b9ad3995ee5fa229035c69013b7dd0d3634b
change-id: 20250128-ringneck-dtbos-98064839355e
prerequisite-change-id: 20250219-pca976x-reset-driver-c9aa95869426:v2
prerequisite-patch-id: 25c49bae002eb11bc6fec479f49f5e3b28b8f403
prerequisite-patch-id: 58e9acffbbd052710bfe672c99ef05f59b1978a6
Best regards,
--
Quentin Schulz <quentin.schulz(a)cherry.de>
commit 318e8c339c9a0891c389298bb328ed0762a9935e upstream.
In [1] the meaning of the synthetic IBPB flags has been redefined for a
better separation of concerns:
- ENTRY_IBPB -- issue IBPB on entry only
- IBPB_ON_VMEXIT -- issue IBPB on VM-Exit only
and the Retbleed mitigations have been updated to match this new
semantics.
Commit [2] was merged shortly before [1], and their interaction was not
handled properly. This resulted in IBPB not being triggered on VM-Exit
in all SRSO mitigation configs requesting an IBPB there.
Specifically, an IBPB on VM-Exit is triggered only when
X86_FEATURE_IBPB_ON_VMEXIT is set. However:
- X86_FEATURE_IBPB_ON_VMEXIT is not set for "spec_rstack_overflow=ibpb",
because before [1] having X86_FEATURE_ENTRY_IBPB was enough. Hence,
an IBPB is triggered on entry but the expected IBPB on VM-exit is
not.
- X86_FEATURE_IBPB_ON_VMEXIT is not set also when
"spec_rstack_overflow=ibpb-vmexit" if X86_FEATURE_ENTRY_IBPB is
already set.
That's because before [1] this was effectively redundant. Hence, e.g.
a "retbleed=ibpb spec_rstack_overflow=bpb-vmexit" config mistakenly
reports the machine still vulnerable to SRSO, despite an IBPB being
triggered both on entry and VM-Exit, because of the Retbleed selected
mitigation config.
- UNTRAIN_RET_VM won't still actually do anything unless
CONFIG_MITIGATION_IBPB_ENTRY is set.
For "spec_rstack_overflow=ibpb", enable IBPB on both entry and VM-Exit
and clear X86_FEATURE_RSB_VMEXIT which is made superfluous by
X86_FEATURE_IBPB_ON_VMEXIT. This effectively makes this mitigation
option similar to the one for 'retbleed=ibpb', thus re-order the code
for the RETBLEED_MITIGATION_IBPB option to be less confusing by having
all features enabling before the disabling of the not needed ones.
For "spec_rstack_overflow=ibpb-vmexit", guard this mitigation setting
with CONFIG_MITIGATION_IBPB_ENTRY to ensure UNTRAIN_RET_VM sequence is
effectively compiled in. Drop instead the CONFIG_MITIGATION_SRSO guard,
since none of the SRSO compile cruft is required in this configuration.
Also, check only that the required microcode is present to effectively
enabled the IBPB on VM-Exit.
Finally, update the KConfig description for CONFIG_MITIGATION_IBPB_ENTRY
to list also all SRSO config settings enabled by this guard.
Fixes: 864bcaa38ee4 ("x86/cpu/kvm: Provide UNTRAIN_RET_VM") [1]
Fixes: d893832d0e1e ("x86/srso: Add IBPB on VMEXIT") [2]
Reported-by: Yosry Ahmed <yosryahmed(a)google.com>
Signed-off-by: Patrick Bellasi <derkling(a)google.com>
Reviewed-by: Borislav Petkov (AMD) <bp(a)alien8.de>
Cc: stable(a)kernel.org
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
---
arch/x86/Kconfig | 3 ++-
arch/x86/kernel/cpu/bugs.c | 21 ++++++++++++++-------
2 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 05c82fd5d0f60..989d432b58345 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2514,7 +2514,8 @@ config CPU_IBPB_ENTRY
depends on CPU_SUP_AMD && X86_64
default y
help
- Compile the kernel with support for the retbleed=ibpb mitigation.
+ Compile the kernel with support for the retbleed=ibpb and
+ spec_rstack_overflow={ibpb,ibpb-vmexit} mitigations.
config CPU_IBRS_ENTRY
bool "Enable IBRS on kernel entry"
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 7b5ba5b8592a2..7df458a6553eb 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1113,6 +1113,8 @@ static void __init retbleed_select_mitigation(void)
case RETBLEED_MITIGATION_IBPB:
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+ mitigate_smt = true;
/*
* IBPB on entry already obviates the need for
@@ -1122,9 +1124,6 @@ static void __init retbleed_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
- setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
- mitigate_smt = true;
-
/*
* There is no need for RSB filling: entry_ibpb() ensures
* all predictions, including the RSB, are invalidated,
@@ -2626,6 +2625,7 @@ static void __init srso_select_mitigation(void)
if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB;
/*
@@ -2635,6 +2635,13 @@ static void __init srso_select_mitigation(void)
*/
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
+
+ /*
+ * There is no need for RSB filling: entry_ibpb() ensures
+ * all predictions, including the RSB, are invalidated,
+ * regardless of IBPB implementation.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
@@ -2643,8 +2650,8 @@ static void __init srso_select_mitigation(void)
break;
case SRSO_CMD_IBPB_ON_VMEXIT:
- if (IS_ENABLED(CONFIG_CPU_SRSO)) {
- if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
+ if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+ if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
@@ -2656,9 +2663,9 @@ static void __init srso_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
- pr_err("WARNING: kernel not compiled with CPU_SRSO.\n");
+ pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
goto pred_cmd;
- }
+ }
break;
default:
--
2.48.1.601.g30ceb7b040-goog
commit 318e8c339c9a0891c389298bb328ed0762a9935e upstream.
In [1] the meaning of the synthetic IBPB flags has been redefined for a
better separation of concerns:
- ENTRY_IBPB -- issue IBPB on entry only
- IBPB_ON_VMEXIT -- issue IBPB on VM-Exit only
and the Retbleed mitigations have been updated to match this new
semantics.
Commit [2] was merged shortly before [1], and their interaction was not
handled properly. This resulted in IBPB not being triggered on VM-Exit
in all SRSO mitigation configs requesting an IBPB there.
Specifically, an IBPB on VM-Exit is triggered only when
X86_FEATURE_IBPB_ON_VMEXIT is set. However:
- X86_FEATURE_IBPB_ON_VMEXIT is not set for "spec_rstack_overflow=ibpb",
because before [1] having X86_FEATURE_ENTRY_IBPB was enough. Hence,
an IBPB is triggered on entry but the expected IBPB on VM-exit is
not.
- X86_FEATURE_IBPB_ON_VMEXIT is not set also when
"spec_rstack_overflow=ibpb-vmexit" if X86_FEATURE_ENTRY_IBPB is
already set.
That's because before [1] this was effectively redundant. Hence, e.g.
a "retbleed=ibpb spec_rstack_overflow=bpb-vmexit" config mistakenly
reports the machine still vulnerable to SRSO, despite an IBPB being
triggered both on entry and VM-Exit, because of the Retbleed selected
mitigation config.
- UNTRAIN_RET_VM won't still actually do anything unless
CONFIG_MITIGATION_IBPB_ENTRY is set.
For "spec_rstack_overflow=ibpb", enable IBPB on both entry and VM-Exit
and clear X86_FEATURE_RSB_VMEXIT which is made superfluous by
X86_FEATURE_IBPB_ON_VMEXIT. This effectively makes this mitigation
option similar to the one for 'retbleed=ibpb', thus re-order the code
for the RETBLEED_MITIGATION_IBPB option to be less confusing by having
all features enabling before the disabling of the not needed ones.
For "spec_rstack_overflow=ibpb-vmexit", guard this mitigation setting
with CONFIG_MITIGATION_IBPB_ENTRY to ensure UNTRAIN_RET_VM sequence is
effectively compiled in. Drop instead the CONFIG_MITIGATION_SRSO guard,
since none of the SRSO compile cruft is required in this configuration.
Also, check only that the required microcode is present to effectively
enabled the IBPB on VM-Exit.
Finally, update the KConfig description for CONFIG_MITIGATION_IBPB_ENTRY
to list also all SRSO config settings enabled by this guard.
Fixes: 864bcaa38ee4 ("x86/cpu/kvm: Provide UNTRAIN_RET_VM") [1]
Fixes: d893832d0e1e ("x86/srso: Add IBPB on VMEXIT") [2]
Reported-by: Yosry Ahmed <yosryahmed(a)google.com>
Signed-off-by: Patrick Bellasi <derkling(a)google.com>
Reviewed-by: Borislav Petkov (AMD) <bp(a)alien8.de>
Cc: stable(a)kernel.org
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
---
arch/x86/Kconfig | 3 ++-
arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++------
2 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0c802ade80406..00ae2e2adcadb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2463,7 +2463,8 @@ config CPU_IBPB_ENTRY
depends on CPU_SUP_AMD && X86_64
default y
help
- Compile the kernel with support for the retbleed=ibpb mitigation.
+ Compile the kernel with support for the retbleed=ibpb and
+ spec_rstack_overflow={ibpb,ibpb-vmexit} mitigations.
config CPU_IBRS_ENTRY
bool "Enable IBRS on kernel entry"
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0b7f6bcbb8ea9..725f827718a71 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1061,6 +1061,8 @@ static void __init retbleed_select_mitigation(void)
case RETBLEED_MITIGATION_IBPB:
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+ mitigate_smt = true;
/*
* IBPB on entry already obviates the need for
@@ -1070,8 +1072,6 @@ static void __init retbleed_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
- mitigate_smt = true;
-
/*
* There is no need for RSB filling: entry_ibpb() ensures
* all predictions, including the RSB, are invalidated,
@@ -2469,6 +2469,7 @@ static void __init srso_select_mitigation(void)
if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB;
/*
@@ -2478,6 +2479,13 @@ static void __init srso_select_mitigation(void)
*/
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
+
+ /*
+ * There is no need for RSB filling: entry_ibpb() ensures
+ * all predictions, including the RSB, are invalidated,
+ * regardless of IBPB implementation.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
@@ -2486,8 +2494,8 @@ static void __init srso_select_mitigation(void)
break;
case SRSO_CMD_IBPB_ON_VMEXIT:
- if (IS_ENABLED(CONFIG_CPU_SRSO)) {
- if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
+ if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+ if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
@@ -2499,9 +2507,9 @@ static void __init srso_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
- pr_err("WARNING: kernel not compiled with CPU_SRSO.\n");
+ pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
goto pred_cmd;
- }
+ }
break;
default:
--
2.48.1.601.g30ceb7b040-goog
commit 318e8c339c9a0891c389298bb328ed0762a9935e upstream.
In [1] the meaning of the synthetic IBPB flags has been redefined for a
better separation of concerns:
- ENTRY_IBPB -- issue IBPB on entry only
- IBPB_ON_VMEXIT -- issue IBPB on VM-Exit only
and the Retbleed mitigations have been updated to match this new
semantics.
Commit [2] was merged shortly before [1], and their interaction was not
handled properly. This resulted in IBPB not being triggered on VM-Exit
in all SRSO mitigation configs requesting an IBPB there.
Specifically, an IBPB on VM-Exit is triggered only when
X86_FEATURE_IBPB_ON_VMEXIT is set. However:
- X86_FEATURE_IBPB_ON_VMEXIT is not set for "spec_rstack_overflow=ibpb",
because before [1] having X86_FEATURE_ENTRY_IBPB was enough. Hence,
an IBPB is triggered on entry but the expected IBPB on VM-exit is
not.
- X86_FEATURE_IBPB_ON_VMEXIT is not set also when
"spec_rstack_overflow=ibpb-vmexit" if X86_FEATURE_ENTRY_IBPB is
already set.
That's because before [1] this was effectively redundant. Hence, e.g.
a "retbleed=ibpb spec_rstack_overflow=bpb-vmexit" config mistakenly
reports the machine still vulnerable to SRSO, despite an IBPB being
triggered both on entry and VM-Exit, because of the Retbleed selected
mitigation config.
- UNTRAIN_RET_VM won't still actually do anything unless
CONFIG_MITIGATION_IBPB_ENTRY is set.
For "spec_rstack_overflow=ibpb", enable IBPB on both entry and VM-Exit
and clear X86_FEATURE_RSB_VMEXIT which is made superfluous by
X86_FEATURE_IBPB_ON_VMEXIT. This effectively makes this mitigation
option similar to the one for 'retbleed=ibpb', thus re-order the code
for the RETBLEED_MITIGATION_IBPB option to be less confusing by having
all features enabling before the disabling of the not needed ones.
For "spec_rstack_overflow=ibpb-vmexit", guard this mitigation setting
with CONFIG_MITIGATION_IBPB_ENTRY to ensure UNTRAIN_RET_VM sequence is
effectively compiled in. Drop instead the CONFIG_MITIGATION_SRSO guard,
since none of the SRSO compile cruft is required in this configuration.
Also, check only that the required microcode is present to effectively
enabled the IBPB on VM-Exit.
Finally, update the KConfig description for CONFIG_MITIGATION_IBPB_ENTRY
to list also all SRSO config settings enabled by this guard.
Fixes: 864bcaa38ee4 ("x86/cpu/kvm: Provide UNTRAIN_RET_VM") [1]
Fixes: d893832d0e1e ("x86/srso: Add IBPB on VMEXIT") [2]
Reported-by: Yosry Ahmed <yosryahmed(a)google.com>
Signed-off-by: Patrick Bellasi <derkling(a)google.com>
Reviewed-by: Borislav Petkov (AMD) <bp(a)alien8.de>
Cc: stable(a)kernel.org
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
---
arch/x86/Kconfig | 3 ++-
arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++------
2 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 49cea5b81649d..ca8dd7e5585f0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2506,7 +2506,8 @@ config CPU_IBPB_ENTRY
depends on CPU_SUP_AMD && X86_64
default y
help
- Compile the kernel with support for the retbleed=ibpb mitigation.
+ Compile the kernel with support for the retbleed=ibpb and
+ spec_rstack_overflow={ibpb,ibpb-vmexit} mitigations.
config CPU_IBRS_ENTRY
bool "Enable IBRS on kernel entry"
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fa2045ad408a7..03221a060ae77 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1092,6 +1092,8 @@ static void __init retbleed_select_mitigation(void)
case RETBLEED_MITIGATION_IBPB:
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+ mitigate_smt = true;
/*
* IBPB on entry already obviates the need for
@@ -1101,8 +1103,6 @@ static void __init retbleed_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
- mitigate_smt = true;
-
/*
* There is no need for RSB filling: entry_ibpb() ensures
* all predictions, including the RSB, are invalidated,
@@ -2607,6 +2607,7 @@ static void __init srso_select_mitigation(void)
if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB;
/*
@@ -2616,6 +2617,13 @@ static void __init srso_select_mitigation(void)
*/
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
+
+ /*
+ * There is no need for RSB filling: entry_ibpb() ensures
+ * all predictions, including the RSB, are invalidated,
+ * regardless of IBPB implementation.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
@@ -2624,8 +2632,8 @@ static void __init srso_select_mitigation(void)
break;
case SRSO_CMD_IBPB_ON_VMEXIT:
- if (IS_ENABLED(CONFIG_CPU_SRSO)) {
- if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
+ if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+ if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
@@ -2637,9 +2645,9 @@ static void __init srso_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
- pr_err("WARNING: kernel not compiled with CPU_SRSO.\n");
+ pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
goto pred_cmd;
- }
+ }
break;
default:
--
2.48.1.601.g30ceb7b040-goog
commit 318e8c339c9a0891c389298bb328ed0762a9935e upstream.
In [1] the meaning of the synthetic IBPB flags has been redefined for a
better separation of concerns:
- ENTRY_IBPB -- issue IBPB on entry only
- IBPB_ON_VMEXIT -- issue IBPB on VM-Exit only
and the Retbleed mitigations have been updated to match this new
semantics.
Commit [2] was merged shortly before [1], and their interaction was not
handled properly. This resulted in IBPB not being triggered on VM-Exit
in all SRSO mitigation configs requesting an IBPB there.
Specifically, an IBPB on VM-Exit is triggered only when
X86_FEATURE_IBPB_ON_VMEXIT is set. However:
- X86_FEATURE_IBPB_ON_VMEXIT is not set for "spec_rstack_overflow=ibpb",
because before [1] having X86_FEATURE_ENTRY_IBPB was enough. Hence,
an IBPB is triggered on entry but the expected IBPB on VM-exit is
not.
- X86_FEATURE_IBPB_ON_VMEXIT is not set also when
"spec_rstack_overflow=ibpb-vmexit" if X86_FEATURE_ENTRY_IBPB is
already set.
That's because before [1] this was effectively redundant. Hence, e.g.
a "retbleed=ibpb spec_rstack_overflow=bpb-vmexit" config mistakenly
reports the machine still vulnerable to SRSO, despite an IBPB being
triggered both on entry and VM-Exit, because of the Retbleed selected
mitigation config.
- UNTRAIN_RET_VM won't still actually do anything unless
CONFIG_MITIGATION_IBPB_ENTRY is set.
For "spec_rstack_overflow=ibpb", enable IBPB on both entry and VM-Exit
and clear X86_FEATURE_RSB_VMEXIT which is made superfluous by
X86_FEATURE_IBPB_ON_VMEXIT. This effectively makes this mitigation
option similar to the one for 'retbleed=ibpb', thus re-order the code
for the RETBLEED_MITIGATION_IBPB option to be less confusing by having
all features enabling before the disabling of the not needed ones.
For "spec_rstack_overflow=ibpb-vmexit", guard this mitigation setting
with CONFIG_MITIGATION_IBPB_ENTRY to ensure UNTRAIN_RET_VM sequence is
effectively compiled in. Drop instead the CONFIG_MITIGATION_SRSO guard,
since none of the SRSO compile cruft is required in this configuration.
Also, check only that the required microcode is present to effectively
enabled the IBPB on VM-Exit.
Finally, update the KConfig description for CONFIG_MITIGATION_IBPB_ENTRY
to list also all SRSO config settings enabled by this guard.
Fixes: 864bcaa38ee4 ("x86/cpu/kvm: Provide UNTRAIN_RET_VM") [1]
Fixes: d893832d0e1e ("x86/srso: Add IBPB on VMEXIT") [2]
Reported-by: Yosry Ahmed <yosryahmed(a)google.com>
Signed-off-by: Patrick Bellasi <derkling(a)google.com>
Reviewed-by: Borislav Petkov (AMD) <bp(a)alien8.de>
Cc: stable(a)kernel.org
Signed-off-by: Linus Torvalds <torvalds(a)linux-foundation.org>
---
arch/x86/Kconfig | 3 ++-
arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++------
2 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2f6312e7ce81f..90ac8d84389cf 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2449,7 +2449,8 @@ config CPU_IBPB_ENTRY
depends on CPU_SUP_AMD && X86_64
default y
help
- Compile the kernel with support for the retbleed=ibpb mitigation.
+ Compile the kernel with support for the retbleed=ibpb and
+ spec_rstack_overflow={ibpb,ibpb-vmexit} mitigations.
config CPU_IBRS_ENTRY
bool "Enable IBRS on kernel entry"
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f84d59cd180b3..dfc02fb32375c 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1092,6 +1092,8 @@ static void __init retbleed_select_mitigation(void)
case RETBLEED_MITIGATION_IBPB:
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+ mitigate_smt = true;
/*
* IBPB on entry already obviates the need for
@@ -1101,8 +1103,6 @@ static void __init retbleed_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
- mitigate_smt = true;
-
/*
* There is no need for RSB filling: entry_ibpb() ensures
* all predictions, including the RSB, are invalidated,
@@ -2607,6 +2607,7 @@ static void __init srso_select_mitigation(void)
if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB;
/*
@@ -2616,6 +2617,13 @@ static void __init srso_select_mitigation(void)
*/
setup_clear_cpu_cap(X86_FEATURE_UNRET);
setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
+
+ /*
+ * There is no need for RSB filling: entry_ibpb() ensures
+ * all predictions, including the RSB, are invalidated,
+ * regardless of IBPB implementation.
+ */
+ setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
@@ -2624,8 +2632,8 @@ static void __init srso_select_mitigation(void)
break;
case SRSO_CMD_IBPB_ON_VMEXIT:
- if (IS_ENABLED(CONFIG_CPU_SRSO)) {
- if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
+ if (IS_ENABLED(CONFIG_CPU_IBPB_ENTRY)) {
+ if (has_microcode) {
setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
@@ -2637,9 +2645,9 @@ static void __init srso_select_mitigation(void)
setup_clear_cpu_cap(X86_FEATURE_RSB_VMEXIT);
}
} else {
- pr_err("WARNING: kernel not compiled with CPU_SRSO.\n");
+ pr_err("WARNING: kernel not compiled with CPU_IBPB_ENTRY.\n");
goto pred_cmd;
- }
+ }
break;
default:
--
2.48.1.601.g30ceb7b040-goog
Please apply this series to the 6.6-stable tree.
This series makes it possible to backport the fix for the BUG_ON
check failure on rename operations reported by syzbot.
The first two patches are for dependency resolution.
Patch 3/3 is the target patch, and it has been tailored to avoid
extensive page/folio conversion.
This patch set has been tested against the latest 6.6.y.
Thanks,
Ryusuke Konishi
Ryusuke Konishi (3):
nilfs2: move page release outside of nilfs_delete_entry and
nilfs_set_link
nilfs2: eliminate staggered calls to kunmap in nilfs_rename
nilfs2: handle errors that nilfs_prepare_chunk() may return
fs/nilfs2/dir.c | 24 +++++++++++-------------
fs/nilfs2/namei.c | 37 ++++++++++++++++++++-----------------
fs/nilfs2/nilfs.h | 10 ++++++++--
3 files changed, 39 insertions(+), 32 deletions(-)
--
2.43.5
The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 47a973fd75639fe80d59f9e1860113bb2a0b112b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025021817-pull-grievance-de31@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 47a973fd75639fe80d59f9e1860113bb2a0b112b Mon Sep 17 00:00:00 2001
From: Kan Liang <kan.liang(a)linux.intel.com>
Date: Wed, 29 Jan 2025 07:48:19 -0800
Subject: [PATCH] perf/x86/intel: Fix ARCH_PERFMON_NUM_COUNTER_LEAF
The EAX of the CPUID Leaf 023H enumerates the mask of valid sub-leaves.
To tell the availability of the sub-leaf 1 (enumerate the counter mask),
perf should check the bit 1 (0x2) of EAS, rather than bit 0 (0x1).
The error is not user-visible on bare metal. Because the sub-leaf 0 and
the sub-leaf 1 are always available. However, it may bring issues in a
virtualization environment when a VMM only enumerates the sub-leaf 0.
Introduce the cpuid35_e?x to replace the macros, which makes the
implementation style consistent.
Fixes: eb467aaac21e ("perf/x86/intel: Support Architectural PerfMon Extension leaf")
Signed-off-by: Kan Liang <kan.liang(a)linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz(a)infradead.org>
Cc: stable(a)vger.kernel.org
Link: https://lkml.kernel.org/r/20250129154820.3755948-3-kan.liang@linux.intel.com
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 966f7832497d..f3d5b718f93f 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -4905,20 +4905,22 @@ static inline bool intel_pmu_broken_perf_cap(void)
static void update_pmu_cap(struct x86_hybrid_pmu *pmu)
{
- unsigned int sub_bitmaps, eax, ebx, ecx, edx;
+ unsigned int cntr, fixed_cntr, ecx, edx;
+ union cpuid35_eax eax;
+ union cpuid35_ebx ebx;
- cpuid(ARCH_PERFMON_EXT_LEAF, &sub_bitmaps, &ebx, &ecx, &edx);
+ cpuid(ARCH_PERFMON_EXT_LEAF, &eax.full, &ebx.full, &ecx, &edx);
- if (ebx & ARCH_PERFMON_EXT_UMASK2)
+ if (ebx.split.umask2)
pmu->config_mask |= ARCH_PERFMON_EVENTSEL_UMASK2;
- if (ebx & ARCH_PERFMON_EXT_EQ)
+ if (ebx.split.eq)
pmu->config_mask |= ARCH_PERFMON_EVENTSEL_EQ;
- if (sub_bitmaps & ARCH_PERFMON_NUM_COUNTER_LEAF_BIT) {
+ if (eax.split.cntr_subleaf) {
cpuid_count(ARCH_PERFMON_EXT_LEAF, ARCH_PERFMON_NUM_COUNTER_LEAF,
- &eax, &ebx, &ecx, &edx);
- pmu->cntr_mask64 = eax;
- pmu->fixed_cntr_mask64 = ebx;
+ &cntr, &fixed_cntr, &ecx, &edx);
+ pmu->cntr_mask64 = cntr;
+ pmu->fixed_cntr_mask64 = fixed_cntr;
}
if (!intel_pmu_broken_perf_cap()) {
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index 1ac79f361645..0ba8d20f2d1d 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -188,11 +188,33 @@ union cpuid10_edx {
* detection/enumeration details:
*/
#define ARCH_PERFMON_EXT_LEAF 0x00000023
-#define ARCH_PERFMON_EXT_UMASK2 0x1
-#define ARCH_PERFMON_EXT_EQ 0x2
-#define ARCH_PERFMON_NUM_COUNTER_LEAF_BIT 0x1
#define ARCH_PERFMON_NUM_COUNTER_LEAF 0x1
+union cpuid35_eax {
+ struct {
+ unsigned int leaf0:1;
+ /* Counters Sub-Leaf */
+ unsigned int cntr_subleaf:1;
+ /* Auto Counter Reload Sub-Leaf */
+ unsigned int acr_subleaf:1;
+ /* Events Sub-Leaf */
+ unsigned int events_subleaf:1;
+ unsigned int reserved:28;
+ } split;
+ unsigned int full;
+};
+
+union cpuid35_ebx {
+ struct {
+ /* UnitMask2 Supported */
+ unsigned int umask2:1;
+ /* EQ-bit Supported */
+ unsigned int eq:1;
+ unsigned int reserved:30;
+ } split;
+ unsigned int full;
+};
+
/*
* Intel Architectural LBR CPUID detection/enumeration details:
*/