Re: [PATCH v3 2/6] x86/bugs: Use SBPB in __write_ibpb() if applicable

[Jim Mattson]

On Wed, Apr 2, 2025 at 11:20 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
>
> __write_ibpb() does IBPB, which (among other things) flushes branch type
> predictions on AMD.  If the CPU has SRSO_NO, or if the SRSO mitigation
> has been disabled, branch type flushing isn't needed, in which case the
> lighter-weight SBPB can be used.

When nested SVM is not supported, should KVM "promote"
SRSO_USER_KERNEL_NO on the host to SRSO_NO in KVM_GET_SUPPORTED_CPUID?
Or is a Linux guest clever enough to do the promotion itself if
CPUID.80000001H:ECX.SVM[bit 2] is clear?