Messages in this thread | | | Date | Mon, 18 Oct 2021 21:37:07 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86/cpu: Fix migration safety with X86_BUG_NULL_SEL |
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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
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