Commit 11cccf5c authored by Ben Gardon's avatar Ben Gardon Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Make TDP MMU root refcount atomic 



In order to parallelize more operations for the TDP MMU, make the
refcount on TDP MMU roots atomic, so that a future patch can allow
multiple threads to take a reference on the root concurrently, while
holding the MMU lock in read mode.

Signed-off-by: default avatarBen Gardon <bgardon@google.com>
Message-Id: <20210401233736.638171-7-bgardon@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent cfc10997

arch/x86/kvm/mmu/mmu_internal.h

+5 −1
Original line number Diff line number Diff line
@@ -50,7 +50,11 @@ struct kvm_mmu_page { 
	u64 *spt;

	/* hold the gfn of each spte inside spt */

	gfn_t *gfns;

	int root_count;          /* Currently serving as active root */

	/* Currently serving as active root */

	union {

		int root_count;

		refcount_t tdp_mmu_root_count;

	};

	unsigned int unsync_children;

	struct kvm_rmap_head parent_ptes; /* rmap pointers to parent sptes */

	DECLARE_BITMAP(unsync_child_bitmap, 512);

arch/x86/kvm/mmu/tdp_mmu.c

+2 −2
Original line number Diff line number Diff line
@@ -56,7 +56,7 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root) 


	lockdep_assert_held_write(&kvm->mmu_lock);



	if (--root->root_count)

	if (!refcount_dec_and_test(&root->tdp_mmu_root_count))

		return;



	WARN_ON(!root->tdp_mmu_page);
@@ -168,7 +168,7 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu) 
	}



	root = alloc_tdp_mmu_page(vcpu, 0, vcpu->arch.mmu->shadow_root_level);

	root->root_count = 1;

	refcount_set(&root->tdp_mmu_root_count, 1);



	list_add(&root->link, &kvm->arch.tdp_mmu_roots);

arch/x86/kvm/mmu/tdp_mmu.h

+7 −3
Original line number Diff line number Diff line
@@ -10,10 +10,14 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu); 
static inline void kvm_tdp_mmu_get_root(struct kvm *kvm,

					struct kvm_mmu_page *root)

{

	BUG_ON(!root->root_count);

	lockdep_assert_held(&kvm->mmu_lock);

	lockdep_assert_held_write(&kvm->mmu_lock);



	++root->root_count;

	/*

	 * This should never fail since roots are removed from the roots

	 * list under the MMU write lock when their reference count falls

	 * to zero.

	 */

	refcount_inc_not_zero(&root->tdp_mmu_root_count);

}



void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root);