Re: [PATCH 3/7] target/i386: Allow MCDT_NO if host supports

[Tao Su <tao1.su@linux.intel.com>]

On Mon, Jun 26, 2023 at 03:03:12PM +0200, Igor Mammedov wrote:
> On Fri, 16 Jun 2023 11:23:07 +0800
> Tao Su <tao1.su@linux.intel.com> wrote:
> 
> > MCDT_NO bit indicates HW contains the security fix and doesn't need to
> > be mitigated to avoid data-dependent behaviour for certain instructions.
> > It needs no hypervisor support. Treat it as supported regardless of what
> > KVM reports.
> > 
> > Signed-off-by: Tao Su <tao1.su@linux.intel.com>
> > Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> > ---
> >  target/i386/kvm/kvm.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> > index de531842f6..4defd8b479 100644
> > --- a/target/i386/kvm/kvm.c
> > +++ b/target/i386/kvm/kvm.c
> > @@ -432,6 +432,11 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
> >          uint32_t eax;
> >          host_cpuid(7, 1, &eax, &unused, &unused, &unused);
> >          ret |= eax & (CPUID_7_1_EAX_FZRM | CPUID_7_1_EAX_FSRS | CPUID_7_1_EAX_FSRC);
> > +    } else if (function == 7 && index == 2 && reg == R_EDX) {
> 
> > +        /* Not new instructions, just an optimization.  */
> comment doesn't make much sense to me, just drop it or
> describe what MCDT_NO is/mitigates.

Ok, I will drop it in the next version, thanks!

> 
> > +        uint32_t edx;
> > +        host_cpuid(7, 2, &unused, &unused, &unused, &edx);
> > +        ret |= edx & CPUID_7_2_EDX_MCDT_NO;
> >      } else if (function == 0xd && index == 0 &&
> >                 (reg == R_EAX || reg == R_EDX)) {
> >          /*
> 
>