Re: [PATCH 16/15] KVM: X86: Update mmu->pdptrs only when it is changed

Paolo Bonzini
2021-12-08T09:09:36Z

On 12/8/21 00:43, Sean Christopherson wrote:
> what guarantees the that PDPTRs in the VMCS are sync'd with
> mmu->pdptrs? I'm not saying they aren't, I just want the changelog
> to prove that they are.

If they aren't synced you should *already* have dirty VCPU_EXREG_PDPTR
and pending KVM_REQ_LOAD_MMU_PGD, shouldn't you? As long as the caching
invariants are respected, this patch is fairly safe, and if they aren't
there are plenty of preexisting bugs anyway.

Paolo

> The next patch does add a fairly heavy unload of the current root for
> !TDP, but that's a bug fix and should be ordered before any
> optimizations anyways.