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

[Igor Mammedov]

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.

> +        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)) {
>          /*