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SubjectRe: [PATCH v2 25/28] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU read lock
Date
On 02/02/21 19:57, Ben Gardon wrote:
> @@ -1485,7 +1489,9 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
> struct kvm_mmu_page *root;
> int root_as_id;
>
> - for_each_tdp_mmu_root_yield_safe(kvm, root, false) {
> + read_lock(&kvm->mmu_lock);
> +
> + for_each_tdp_mmu_root_yield_safe(kvm, root, true) {
> root_as_id = kvm_mmu_page_as_id(root);
> if (root_as_id != slot->as_id)
> continue;
> @@ -1493,6 +1499,8 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
> zap_collapsible_spte_range(kvm, root, slot->base_gfn,
> slot->base_gfn + slot->npages);
> }
> +
> + read_unlock(&kvm->mmu_lock);
> }


I'd prefer the functions to be consistent about who takes the lock,
either mmu.c or tdp_mmu.c. Since everywhere else you're doing it in
mmu.c, that would be:

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 0554d9c5c5d4..386ee4b703d9 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5567,10 +5567,13 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
write_lock(&kvm->mmu_lock);
slot_handle_leaf(kvm, (struct kvm_memory_slot *)memslot,
kvm_mmu_zap_collapsible_spte, true);
+ write_unlock(&kvm->mmu_lock);

- if (kvm->arch.tdp_mmu_enabled)
+ if (kvm->arch.tdp_mmu_enabled) {
+ read_lock(&kvm->mmu_lock);
kvm_tdp_mmu_zap_collapsible_sptes(kvm, memslot);
- write_unlock(&kvm->mmu_lock);
+ read_unlock(&kvm->mmu_lock);
+ }
}

void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm,
and just lockdep_assert_held_read here.

> - tdp_mmu_set_spte(kvm, &iter, 0);
> -
> - spte_set = true;

Is it correct to remove this assignment?

Paolo

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