Re: [RFC PATCH 09/11] x86: Migrate spec_ctrl vendor checks to x86_vendor_is()

[Alejandro Vallejo <alejandro.garciavallejo@amd.com>]

On Thu Dec 11, 2025 at 4:38 PM CET, Andrew Cooper wrote:
> On 11/12/2025 10:31 am, Alejandro Vallejo wrote:
>> Seeing how both you and Andrew seem onboard with dropping cross-vendor support
>
> I found another cross-vendor dropping which you'll want to look into.
>
> struct svm_vcpu contains three guest_sysenter_* MSRs.
>
> In AMD CPUs, these MSRs only have 32 bits of storage, with the upper
> halfs write-discard.  They are switched via VMLOAD/VMSAVE.
>
> However, in the cross-vendor case, the upper halves are needed for 64bit
> kernels setting up SYSENTER support.  Therefore, they're unconditionally
> intercepted so we can avoid losing the upper half.
>
> By dropping cross-vendor support, we can get rid of these fields, allow
> the guest unconditional access, and simply the MSR intercept logic a little.
>
> ~Andrew

Sounds straightforward, I'll add it to the pile.

Cheers,
Alejandro