Re: [PATCH 3/3] KVM: x86/mmu: Stop zapping invalidated TDP MMU roots asynchronously

[Paolo Bonzini]

On 9/16/23 02:39, Sean Christopherson wrote:
> +		if (!root->tdp_mmu_scheduled_root_to_zap)
> +			continue;
> +
> +		root->tdp_mmu_scheduled_root_to_zap = false;

This is protected by slots_lock... tricky.

Worth squashing in a comment and also a small update to another comment:

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index 93b9d50c24ad..decc1f153669 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -60,6 +60,8 @@ struct kvm_mmu_page {
 	bool unsync;
 	union {
 		u8 mmu_valid_gen;
+
+		/* Only accessed under slots_lock.  */
 		bool tdp_mmu_scheduled_root_to_zap;
 	};
 
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index ca3304c2c00c..070ee5b2c271 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -246,7 +246,7 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
 	 * by a memslot update or by the destruction of the VM.  Initialize the
 	 * refcount to two; one reference for the vCPU, and one reference for
 	 * the TDP MMU itself, which is held until the root is invalidated and
-	 * is ultimately put by tdp_mmu_zap_root_work().
+	 * is ultimately put by kvm_tdp_mmu_zap_invalidated_roots().
 	 */
 	refcount_set(&root->tdp_mmu_root_count, 2);
 

Paolo

> +		KVM_BUG_ON(!root->role.invalid, kvm);