Re: [PATCH 01/12] x86: Reject CPU policies with vendors other than the host's

["Roger Pau Monné" <roger.pau@citrix.com>]

On Fri, Feb 06, 2026 at 05:15:23PM +0100, Alejandro Vallejo wrote:
> While in principle it's possible to have a vendor virtualising another,
> this is fairly tricky in practice. Not doing so enables certain
> optimisations with regards to vendor checks in later patches.
> 
> Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@amd.com>
> ---
> Patch 1 from the cross-vendor series. Do not merge here. It's simply for
> consistency.
> ---
>  xen/lib/x86/policy.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/lib/x86/policy.c b/xen/lib/x86/policy.c
> index f033d22785..079c42a29b 100644
> --- a/xen/lib/x86/policy.c
> +++ b/xen/lib/x86/policy.c
> @@ -15,7 +15,8 @@ int x86_cpu_policies_are_compatible(const struct cpu_policy *host,
>  #define FAIL_MSR(m) \
>      do { e.msr = (m); goto out; } while ( 0 )
>  
> -    if ( guest->basic.max_leaf > host->basic.max_leaf )
> +    if ( (guest->x86_vendor     != host->x86_vendor) ||
> +         (guest->basic.max_leaf >  host->basic.max_leaf) )

You possibly want to expand test-cpu-policy.c to add a small test to
ensure this works as expected?  Not that it shouldn't, but it's
trivial to expand test_is_compatible_{success,failure}() to add a
small test for the vendor checking.

Thanks, Roger.