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

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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: Ben Gardon <bgardon@google.com>
Message-Id: <20210401233736.638171-7-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Ben Gardon
2021-04-01 16:37:29 -07:00
committed by Paolo Bonzini
parent cfc109979b
commit 11cccf5c04
3 changed files with 14 additions and 6 deletions
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6
arch/x86/kvm/mmu/mmu_internal.h
View File

@@ -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);

4
arch/x86/kvm/mmu/tdp_mmu.c
View File

@@ -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);

10
arch/x86/kvm/mmu/tdp_mmu.h
View File

@@ -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);