Re: [PATCH v2 2/7] KVM: x86: Add helpers to perform CPUID-based guest vendor check

[Jim Mattson]

On Wed, Mar 4, 2020 at 5:34 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> Add helpers to provide CPUID-based guest vendor checks, i.e. to do the
> ugly register comparisons.  Use the new helpers to check for an AMD
> guest vendor in guest_cpuid_is_amd() as well as in the existing emulator
> flows.
>
> Using the new helpers fixes a _very_ theoretical bug where
> guest_cpuid_is_amd() would get a false positive on a non-AMD virtual CPU
> with a vendor string beginning with "Auth" due to the previous logic
> only checking EBX.  It also fixes a marginally less theoretically bug
> where guest_cpuid_is_amd() would incorrectly return false for a guest
> CPU with "AMDisbetter!" as its vendor string.
>
> Fixes: a0c0feb57992c ("KVM: x86: reserve bit 8 of non-leaf PDPEs and PML4Es in 64-bit mode on AMD")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>