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@xxxxxxxxxxxxx>
