Re: [PATCH 09/12] KVM: MMU: look for a cached PGD when going from 32-bit to 64-bit

Sean Christopherson
2022-02-11T17:38:13Z

On Fri, Feb 11, 2022, Paolo Bonzini wrote:
> On 2/11/22 02:32, Sean Christopherson wrote:
> > Maybe cached_root_find_and_rotate() or cached_root_find_and_age()?
>
> I'll go for cached_root_find_and_keep_current() and
> cached_root_find_without_current(), respectively.
>
> >
> > Hmm, while we're refactoring this, I'd really prefer we not grab vcpu->arch.mmu
> > way down in the helpers. @vcpu is needed only for the request, so what about
> > doing this?
> >
> > if (!fast_pgd_switch(vcpu, new_pgd, new_role)) {
> > /*
> > * <whatever kvm_mmu_reload() becomes> will set up a new root
> > * prior to the next VM-Enter. Free the current root if it's
> > * valid, i.e. if a valid root was evicted from the cache.
> > */
> > if (VALID_PAGE(vcpu->arch.mmu->root.hpa))
> > kvm_mmu_free_roots(vcpu, vcpu->arch.mmu, KVM_MMU_ROOT_CURRENT);
> > return;
> > }
>
> I tried, but it's much easier to describe the cache functions if their
> common postcondition is "vcpu->arch.mmu->root.hpa is never stale"; which
> requires not a struct kvm_vcpu* but at least a struct kvm*, for the MMU
> lock.
>
> I could change kvm_mmu_free_roots and cached_root_* to take a struct kvm*
> plus a struct kvm_mmu*. Does that sound better?

Ya, works for me, thanks!