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

Paolo Bonzini
2022-02-11T11:45:36Z

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?

Paolo