On 10/3/23 02:28, Jinank Jain wrote: ... > diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c > index 2eabccde94fb..92350a24848c 100644 > --- a/arch/x86/kernel/sev-shared.c > +++ b/arch/x86/kernel/sev-shared.c > @@ -880,6 +880,9 @@ static enum es_result vc_handle_cpuid(struct ghcb *ghcb, > if (snp_cpuid_ret != -EOPNOTSUPP) > return ES_VMM_ERROR; > > + if (regs->ax == 0xD && regs->cx == 0x1) > + ghcb_set_xss(ghcb, 0); The spec talks about leaf 0xD, but not the subleaf: > XSS is only required to besupplied when a request forCPUID 0000_000D > is made andthe guest supports the XSS MSR(0x0000_0DA0). Why restrict this to subleaf (regx->cx) 1? Second, XCR0 is being supplied regardless of the CPUID leaf. Why should XSS be restricted to 0xD while XCR0 is universally supplied? Third, why is it OK to supply a garbage (0) value? If the GHCB field is required it's surely because the host *NEEDS* the value to do something. Won't a garbage value potentially confuse the host?
