4.4-stable review patch. If anyone has any objections, please let me know.
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From: Hugh Dickins hughd@google.com
Why was 4 chosen for kernel PCID and 6 for user PCID? No good reason in a backport where PCIDs are only used for Kaiser.
If we continue with those, then we shall need to add Andy Lutomirski's 4.13 commit 6c690ee1039b ("x86/mm: Split read_cr3() into read_cr3_pa() and __read_cr3()"), which deals with the problem of read_cr3() callers finding stray bits in the cr3 that they expected to be page-aligned; and for hibernation, his 4.14 commit f34902c5c6c0 ("x86/hibernate/64: Mask off CR3's PCID bits in the saved CR3").
But if 0 is used for kernel PCID, then there's no need to add in those commits - whenever the kernel looks, it sees 0 in the lower bits; and 0 for kernel seems an obvious choice.
And I naughtily propose 128 for user PCID. Because there's a place in _SWITCH_TO_USER_CR3 where it takes note of the need for TLB FLUSH, but needs to reset that to NOFLUSH for the next occasion. Currently it does so with a "movb $(0x80)" into the high byte of the per-cpu quadword, but that will cause a machine without PCID support to crash. Now, if %al just happened to have 0x80 in it at that point, on a machine with PCID support, but 0 on a machine without PCID support...
(That will go badly wrong once the pgd can be at a physical address above 2^56, but even with 5-level paging, physical goes up to 2^52.)
Signed-off-by: Hugh Dickins hughd@google.com Acked-by: Jiri Kosina jkosina@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/kaiser.h | 19 ++++++++++++------- arch/x86/include/asm/pgtable_types.h | 7 ++++--- arch/x86/mm/tlb.c | 3 +++ 3 files changed, 19 insertions(+), 10 deletions(-)
--- a/arch/x86/include/asm/kaiser.h +++ b/arch/x86/include/asm/kaiser.h @@ -29,14 +29,19 @@ orq X86_CR3_PCID_KERN_VAR, \reg movq \reg, %cr3 .endm
-.macro _SWITCH_TO_USER_CR3 reg +.macro _SWITCH_TO_USER_CR3 reg regb +/* + * regb must be the low byte portion of reg: because we have arranged + * for the low byte of the user PCID to serve as the high byte of NOFLUSH + * (0x80 for each when PCID is enabled, or 0x00 when PCID and NOFLUSH are + * not enabled): so that the one register can update both memory and cr3. + */ movq %cr3, \reg andq $(~(X86_CR3_PCID_ASID_MASK | KAISER_SHADOW_PGD_OFFSET)), \reg orq PER_CPU_VAR(X86_CR3_PCID_USER_VAR), \reg js 9f -// FLUSH this time, reset to NOFLUSH for next time -// But if nopcid? Consider using 0x80 for user pcid? -movb $(0x80), PER_CPU_VAR(X86_CR3_PCID_USER_VAR+7) +/* FLUSH this time, reset to NOFLUSH for next time (if PCID enabled) */ +movb \regb, PER_CPU_VAR(X86_CR3_PCID_USER_VAR+7) 9: movq \reg, %cr3 .endm @@ -49,7 +54,7 @@ popq %rax
.macro SWITCH_USER_CR3 pushq %rax -_SWITCH_TO_USER_CR3 %rax +_SWITCH_TO_USER_CR3 %rax %al popq %rax .endm
@@ -61,7 +66,7 @@ movq PER_CPU_VAR(unsafe_stack_register_b
.macro SWITCH_USER_CR3_NO_STACK movq %rax, PER_CPU_VAR(unsafe_stack_register_backup) -_SWITCH_TO_USER_CR3 %rax +_SWITCH_TO_USER_CR3 %rax %al movq PER_CPU_VAR(unsafe_stack_register_backup), %rax .endm
@@ -69,7 +74,7 @@ movq PER_CPU_VAR(unsafe_stack_register_b
.macro SWITCH_KERNEL_CR3 reg .endm -.macro SWITCH_USER_CR3 reg +.macro SWITCH_USER_CR3 reg regb .endm .macro SWITCH_USER_CR3_NO_STACK .endm --- a/arch/x86/include/asm/pgtable_types.h +++ b/arch/x86/include/asm/pgtable_types.h @@ -111,16 +111,17 @@
/* Mask for all the PCID-related bits in CR3: */ #define X86_CR3_PCID_MASK (X86_CR3_PCID_NOFLUSH | X86_CR3_PCID_ASID_MASK) +#define X86_CR3_PCID_ASID_KERN (_AC(0x0,UL)) + #if defined(CONFIG_KAISER) && defined(CONFIG_X86_64) -#define X86_CR3_PCID_ASID_KERN (_AC(0x4,UL)) -#define X86_CR3_PCID_ASID_USER (_AC(0x6,UL)) +/* Let X86_CR3_PCID_ASID_USER be usable for the X86_CR3_PCID_NOFLUSH bit */ +#define X86_CR3_PCID_ASID_USER (_AC(0x80,UL))
#define X86_CR3_PCID_KERN_FLUSH (X86_CR3_PCID_ASID_KERN) #define X86_CR3_PCID_USER_FLUSH (X86_CR3_PCID_ASID_USER) #define X86_CR3_PCID_KERN_NOFLUSH (X86_CR3_PCID_NOFLUSH | X86_CR3_PCID_ASID_KERN) #define X86_CR3_PCID_USER_NOFLUSH (X86_CR3_PCID_NOFLUSH | X86_CR3_PCID_ASID_USER) #else -#define X86_CR3_PCID_ASID_KERN (_AC(0x0,UL)) #define X86_CR3_PCID_ASID_USER (_AC(0x0,UL)) /* * PCIDs are unsupported on 32-bit and none of these bits can be --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -50,6 +50,9 @@ static void load_new_mm_cr3(pgd_t *pgdir * invpcid_flush_single_context(X86_CR3_PCID_ASID_USER) could * do it here, but can only be used if X86_FEATURE_INVPCID is * available - and many machines support pcid without invpcid. + * + * The line below is a no-op: X86_CR3_PCID_KERN_FLUSH is now 0; + * but keep that line in there in case something changes. */ new_mm_cr3 |= X86_CR3_PCID_KERN_FLUSH; kaiser_flush_tlb_on_return_to_user();