On Mon, Oct 18, 2021 at 07:29:41PM +0000, Sean Christopherson wrote:
> This isn't correct. When running as a guest, the intended behavior is to fully
> trust the CPUID.0x80000021 bit.
Really? Because I'm coming from an SEV-SNP mail thread where we don't
trust the HV at all and we even hand in a CPUID page into the guest...
:-P
> If bit 6 is set, yay, the hypervisor has told the kernel that it
> will only ever run on hardware without the bug. If bit 6 is clear
> and HYPERVISOR is true, then the FMS crud can't be trusted because
> the kernel _may_ run on affected hardware in the future even if the
> current underlying hardware is not affected.
Ok, I see, then the CPUID check needs to go first, makes sense.
> I agree. If the argument for this patch is that the kernel can be migrated to
> older hardware, then it stands to reason that the kernel could also be migrated
> to a different CPU vendor entirely. E.g. start on Intel, migrate to Zen1, kaboom.
Migration across vendors? Really, that works?
I'll believe it only when I see it with my own eyes.
:-)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
