Il ven 28 giu 2024, 10:32 Xiaoyao Li <xiaoyao...@intel.com> ha scritto:
> On 6/27/2024 10:06 PM, Paolo Bonzini wrote:
> > The recent addition of the SUCCOR bit to kvm_arch_get_supported_cpuid()
> > causes the bit to be visible when "-cpu host" VMs are started on Intel
> > processors.
> >
> > While this should in principle be harmless, it's not tidy and we don't
> > even know for sure that it doesn't cause any guest OS to take unexpected
> > paths. Since x86_cpu_get_supported_feature_word() can return different
> > different values depending on the guest, adjust it to hide the SUCCOR
>
> superfluous different
>
> > bit if the guest has non-AMD vendor.
>
> It seems to adjust it based on vendor in kvm_arch_get_supported_cpuid()
> is better than in x86_cpu_get_supported_feature_word(). Otherwise
> kvm_arch_get_supported_cpuid() still returns "risky" value for Intel VMs.
>
But the cpuid bit is only invalid for Intel *guest* vendor, not host. It is
not a problem to have it if you run on Intel host but have a guest model
with AMD vendor.
I will check if there are other callers of kvm_arch_get_supported_cpuid(),
or callers of x86_cpu_get_supported_feature_word() with NULL cpu, that
might care about the difference.
Paolo
>
> > Suggested-by: Xiaoyao Li <xiaoyao...@intel.com>
> > Cc: John Allen <john.al...@amd.com>
> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> > ---
> > target/i386/cpu.c | 16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index deb58670651..f3e9b543682 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -6064,8 +6064,10 @@ uint64_t
> x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w)
> > } else {
> > return ~0;
> > }
> > +
> > + switch (w) {
> > #ifndef TARGET_X86_64
> > - if (w == FEAT_8000_0001_EDX) {
> > + case FEAT_8000_0001_EDX:
> > /*
> > * 32-bit TCG can emulate 64-bit compatibility mode. If there
> is no
> > * way for userspace to get out of its 32-bit jail, we can
> leave
> > @@ -6077,6 +6079,18 @@ uint64_t
> x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w)
> > r &= ~unavail;
> > break;
> > #endif
> > +
> > + case FEAT_8000_0007_EBX:
> > + if (cpu && !IS_AMD_CPU(&cpu->env)) {
> > + /* Disable AMD machine check architecture for Intel CPU. */
> > + r = 0;
> > + }
> > + break;
> > +
> > + default:
> > + break;
> > + }
> > +
> > if (cpu && cpu->migratable) {
> > r &= x86_cpu_get_migratable_flags(w);
> > }
>
>
