KVM does not implement MSR_IA32_TSX_CTRL, so it must not be presented to the guests. It is also confusing to have !ARCH_CAP_TSX_CTRL_MSR && !RTM && ARCH_CAP_TAA_NO: lack of MSR_IA32_TSX_CTRL suggests TSX was not hidden (it actually was), yet the value says that TSX is not vulnerable to microarchitectural data sampling. Fix both.
Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com --- arch/x86/kvm/x86.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 5d530521f11d..6ea735d632e9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1327,12 +1327,18 @@ static u64 kvm_get_arch_capabilities(void) * If TSX is disabled on the system, guests are also mitigated against * TAA and clear CPU buffer mitigation is not required for guests. */ - if (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM) && - (data & ARCH_CAP_TSX_CTRL_MSR)) + if (!boot_cpu_has(X86_FEATURE_RTM)) + data &= ~ARCH_CAP_TAA_NO; + else if (!boot_cpu_has_bug(X86_BUG_TAA)) + data |= ARCH_CAP_TAA_NO; + else if (data & ARCH_CAP_TSX_CTRL_MSR) data &= ~ARCH_CAP_MDS_NO;
+ /* KVM does not emulate MSR_IA32_TSX_CTRL. */ + data &= ~ARCH_CAP_TSX_CTRL_MSR; return data; } +EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
static int kvm_get_msr_feature(struct kvm_msr_entry *msr) {
On Mon, Nov 18, 2019 at 10:17 AM Paolo Bonzini pbonzini@redhat.com wrote:
KVM does not implement MSR_IA32_TSX_CTRL, so it must not be presented to the guests. It is also confusing to have !ARCH_CAP_TSX_CTRL_MSR && !RTM && ARCH_CAP_TAA_NO: lack of MSR_IA32_TSX_CTRL suggests TSX was not hidden (it actually was), yet the value says that TSX is not vulnerable to microarchitectural data sampling. Fix both.
I actually think kvm should virtualize IA32_TSX_CTRL for VMs that have exclusive use of their cores (i.e. the same VMs for which we disable MWAIT and HLT exiting).
On Mon, Nov 18, 2019 at 10:17 AM Paolo Bonzini pbonzini@redhat.com wrote:
KVM does not implement MSR_IA32_TSX_CTRL, so it must not be presented to the guests. It is also confusing to have !ARCH_CAP_TSX_CTRL_MSR && !RTM && ARCH_CAP_TAA_NO: lack of MSR_IA32_TSX_CTRL suggests TSX was not hidden (it actually was), yet the value says that TSX is not vulnerable to microarchitectural data sampling. Fix both. Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com
Ignore my previous comment. I see that the functionality I want is coming later in this series.
Reviewed-by: Jim Mattson jmattson@google.com
On Mon, Nov 18, 2019 at 07:17:43PM +0100, Paolo Bonzini wrote:
KVM does not implement MSR_IA32_TSX_CTRL, so it must not be presented to the guests. It is also confusing to have !ARCH_CAP_TSX_CTRL_MSR && !RTM && ARCH_CAP_TAA_NO: lack of MSR_IA32_TSX_CTRL suggests TSX was not hidden (it actually was), yet the value says that TSX is not vulnerable to microarchitectural data sampling. Fix both.
Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini pbonzini@redhat.com
arch/x86/kvm/x86.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 5d530521f11d..6ea735d632e9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1327,12 +1327,18 @@ static u64 kvm_get_arch_capabilities(void) * If TSX is disabled on the system, guests are also mitigated against * TAA and clear CPU buffer mitigation is not required for guests. */
- if (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM) &&
(data & ARCH_CAP_TSX_CTRL_MSR))
- if (!boot_cpu_has(X86_FEATURE_RTM))
data &= ~ARCH_CAP_TAA_NO;- else if (!boot_cpu_has_bug(X86_BUG_TAA))
data |= ARCH_CAP_TAA_NO;- else if (data & ARCH_CAP_TSX_CTRL_MSR) data &= ~ARCH_CAP_MDS_NO;
- /* KVM does not emulate MSR_IA32_TSX_CTRL. */
- data &= ~ARCH_CAP_TSX_CTRL_MSR; return data;
} +EXPORT_SYMBOL_GPL(kvm_get_arch_capabilities);
Whoever backports this patch should drop this spurious addition of EXPORT_SYMBOL_GPL, unless they also want to backport the cleanup :-).
linux-stable-mirror@lists.linaro.org
-
Jim Mattson -
Paolo Bonzini -
Sean Christopherson