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

[Paolo Bonzini]

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.