Re: [PATCH v3 5/5] KVM: SVM: Enable shadow stack virtualization for SVM

[John Allen <john.allen@amd.com>]

On Mon, Aug 25, 2025 at 09:33:09AM +0800, Chao Gao wrote:
> On Wed, Aug 06, 2025 at 08:45:10PM +0000, John Allen wrote:
> >Remove the explicit clearing of shadow stack CPU capabilities.
> >
> >Signed-off-by: John Allen <john.allen@amd.com>
> >---
> >v3:
> >  - New in v3.
> >---
> > arch/x86/kvm/svm/svm.c | 5 -----
> > 1 file changed, 5 deletions(-)
> >
> >diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> >index 82cde3578c96..b67aa546d8f4 100644
> >--- a/arch/x86/kvm/svm/svm.c
> >+++ b/arch/x86/kvm/svm/svm.c
> >@@ -5255,11 +5255,6 @@ static __init void svm_set_cpu_caps(void)
> > 	kvm_set_cpu_caps();
> > 
> > 	kvm_caps.supported_perf_cap = 0;
> >-	kvm_caps.supported_xss = 0;
> >-
> >-	/* KVM doesn't yet support CET virtualization for SVM. */
> >-	kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
> >-	kvm_cpu_cap_clear(X86_FEATURE_IBT);
> 
> IIUC, IBT should be cleared because KVM doesn't support IBT for SVM.

Yeah, I wondered about this. The reason I chose to not clear this is
because we don't explicitly clear other features that are not supported
on AMD hardware AFAICT. Is there a reason we should clear this and not
other unsupported features?

Thanks,
John