| Message ID | 20240823185323.2563194-1-jmattson@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Distinguish between variants of IBPB | expand |
On 8/23/24 13:53, Jim Mattson wrote: > Prior to Zen4, AMD's IBPB did not flush the RAS (or, in Intel > terminology, the RSB). Hence, the older version of AMD's IBPB was not > equivalent to Intel's IBPB. However, KVM has been treating them as > equivalent, synthesizing Intel's CPUID.(EAX=7,ECX=0):EDX[bit 26] on any > platform that supports the synthetic features X86_FEATURE_IBPB and > X86_FEATURE_IBRS. > > Equivalence also requires a previously ignored feature on the AMD side, > CPUID Fn8000_0008_EBX[IBPB_RET], which is enumerated on Zen4. > > v3: Pass through IBPB_RET from hardware to userspace. [Tom] > Derive AMD_IBPB from X86_FEATURE_SPEC_CTRL rather than > X86_FEATURE_IBPB. [Tom] > Clarify semantics of X86_FEATURE_IBPB. > > v2: Use IBPB_RET to identify semantic equality. [Venkatesh] > > Jim Mattson (4): > x86/cpufeatures: Clarify semantics of X86_FEATURE_IBPB > x86/cpufeatures: Define X86_FEATURE_AMD_IBPB_RET > KVM: x86: Advertise AMD_IBPB_RET to userspace > KVM: x86: AMD's IBPB is not equivalent to Intel's IBPB > > arch/x86/include/asm/cpufeatures.h | 3 ++- > arch/x86/kvm/cpuid.c | 8 ++++++-- > 2 files changed, 8 insertions(+), 3 deletions(-) For the series: Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> >
On Fri, Aug 23 2024 at 11:53, Jim Mattson wrote: > Prior to Zen4, AMD's IBPB did not flush the RAS (or, in Intel > terminology, the RSB). Hence, the older version of AMD's IBPB was not > equivalent to Intel's IBPB. However, KVM has been treating them as > equivalent, synthesizing Intel's CPUID.(EAX=7,ECX=0):EDX[bit 26] on any > platform that supports the synthetic features X86_FEATURE_IBPB and > X86_FEATURE_IBRS. > > Equivalence also requires a previously ignored feature on the AMD side, > CPUID Fn8000_0008_EBX[IBPB_RET], which is enumerated on Zen4. > > v3: Pass through IBPB_RET from hardware to userspace. [Tom] > Derive AMD_IBPB from X86_FEATURE_SPEC_CTRL rather than > X86_FEATURE_IBPB. [Tom] > Clarify semantics of X86_FEATURE_IBPB. > > v2: Use IBPB_RET to identify semantic equality. [Venkatesh] Assuming this goes through the KVM tree: Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Prior to Zen4, AMD's IBPB did not flush the RAS (or, in Intel terminology, the RSB). Hence, the older version of AMD's IBPB was not equivalent to Intel's IBPB. However, KVM has been treating them as equivalent, synthesizing Intel's CPUID.(EAX=7,ECX=0):EDX[bit 26] on any platform that supports the synthetic features X86_FEATURE_IBPB and X86_FEATURE_IBRS. Equivalence also requires a previously ignored feature on the AMD side, CPUID Fn8000_0008_EBX[IBPB_RET], which is enumerated on Zen4. v3: Pass through IBPB_RET from hardware to userspace. [Tom] Derive AMD_IBPB from X86_FEATURE_SPEC_CTRL rather than X86_FEATURE_IBPB. [Tom] Clarify semantics of X86_FEATURE_IBPB. v2: Use IBPB_RET to identify semantic equality. [Venkatesh] Jim Mattson (4): x86/cpufeatures: Clarify semantics of X86_FEATURE_IBPB x86/cpufeatures: Define X86_FEATURE_AMD_IBPB_RET KVM: x86: Advertise AMD_IBPB_RET to userspace KVM: x86: AMD's IBPB is not equivalent to Intel's IBPB arch/x86/include/asm/cpufeatures.h | 3 ++- arch/x86/kvm/cpuid.c | 8 ++++++-- 2 files changed, 8 insertions(+), 3 deletions(-)