Re: [PATCH 1/2] KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot change

Yan Zhao
2022-11-10T02:50:04Z

On Thu, Nov 10, 2022 at 01:48:20AM +0000, Sean Christopherson wrote:
> Call kvm_mmu_zap_all_fast() directly when flushing a memslot instead of
> bounding through the page-track mechanism. KVM (unfortunately) needs to
> zap and flush all page tables on memslot DELETE/MOVE irrespective of
> whether KVM is shadowing guest page tables.
>
> This will allow changing KVM to register a page-track notifier on the
> first shadow root allocation, and will also allow deleting the misguided
> kvm_page_track_flush_slot() hook itself once KVM-GT also moves to a
> different method for reacting to memslot changes.
>
<...>
> @@ -6021,7 +6014,6 @@ int kvm_mmu_init_vm(struct kvm *kvm)
> return r;
>
> node->track_write = kvm_mmu_pte_write;
> - node->track_flush_slot = kvm_mmu_invalidate_zap_pages_in_memslot;
> kvm_page_track_register_notifier(kvm, node);
>
> kvm->arch.split_page_header_cache.kmem_cache = mmu_page_header_cache;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e46e458c5b08..5da86fe3c113 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12550,6 +12550,8 @@ void kvm_arch_flush_shadow_all(struct kvm *kvm)
> void kvm_arch_flush_shadow_memslot(struct kvm *kvm,
> struct kvm_memory_slot *slot)
> {
> + kvm_mmu_zap_all_fast(kvm);
> +
> kvm_page_track_flush_slot(kvm, slot);
Could we move this kvm_page_track_flush_slot() to right before
kvm_commit_memory_region()?
As KVM now does not need track_flush_slot any more and kvmgt is the only user
to track_flush_slot, we can rename it to track_slot_changed to notify
the new/deleted/moved slot.
Do you think it's good?

Thanks
Yan

> }
>
> --
> 2.38.1.431.g37b22c650d-goog
>