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Subject[PATCH 22/22] kvm: mmu: Don't clear write flooding count for direct roots
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Direct roots don't have a write flooding count because the guest can't
affect that paging structure. Thus there's no need to clear the write
flooding count on a fast CR3 switch for direct roots.

Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
machine. This series introduced no new failures.

This series can be viewed in Gerrit at:
https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538

Signed-off-by: Ben Gardon <bgardon@google.com>
---
arch/x86/kvm/mmu/mmu.c | 15 +++++++++++----
arch/x86/kvm/mmu/tdp_mmu.c | 12 ++++++++++++
arch/x86/kvm/mmu/tdp_mmu.h | 2 ++
3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 0ce7720a72d4e..345c934fabf4c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4267,7 +4267,8 @@ static void nonpaging_init_context(struct kvm_vcpu *vcpu,
context->nx = false;
}

-static inline bool is_root_usable(struct kvm_mmu_root_info *root, gpa_t pgd,
+static inline bool is_root_usable(struct kvm *kvm,
+ struct kvm_mmu_root_info *root, gpa_t pgd,
union kvm_mmu_page_role role)
{
return (role.direct || pgd == root->pgd) &&
@@ -4293,13 +4294,13 @@ static bool cached_root_available(struct kvm_vcpu *vcpu, gpa_t new_pgd,
root.pgd = mmu->root_pgd;
root.hpa = mmu->root_hpa;

- if (is_root_usable(&root, new_pgd, new_role))
+ if (is_root_usable(vcpu->kvm, &root, new_pgd, new_role))
return true;

for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) {
swap(root, mmu->prev_roots[i]);

- if (is_root_usable(&root, new_pgd, new_role))
+ if (is_root_usable(vcpu->kvm, &root, new_pgd, new_role))
break;
}

@@ -4356,7 +4357,13 @@ static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd,
*/
vcpu_clear_mmio_info(vcpu, MMIO_GVA_ANY);

- __clear_sp_write_flooding_count(to_shadow_page(vcpu->arch.mmu->root_hpa));
+ /*
+ * If this is a direct root page, it doesn't have a write flooding
+ * count. Otherwise, clear the write flooding count.
+ */
+ if (!new_role.direct)
+ __clear_sp_write_flooding_count(
+ to_shadow_page(vcpu->arch.mmu->root_hpa));
}

void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd, bool skip_tlb_flush,
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 42dde27decd75..c07831b0c73e1 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -124,6 +124,18 @@ static struct kvm_mmu_page *find_tdp_mmu_root_with_role(
return NULL;
}

+hpa_t kvm_tdp_mmu_root_hpa_for_role(struct kvm *kvm,
+ union kvm_mmu_page_role role)
+{
+ struct kvm_mmu_page *root;
+
+ root = find_tdp_mmu_root_with_role(kvm, role);
+ if (root)
+ return __pa(root->spt);
+
+ return INVALID_PAGE;
+}
+
static union kvm_mmu_page_role page_role_for_level(struct kvm_vcpu *vcpu,
int level)
{
diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index cc0b7241975aa..2395ffa71bb05 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -9,6 +9,8 @@ void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);

bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
+hpa_t kvm_tdp_mmu_root_hpa_for_role(struct kvm *kvm,
+ union kvm_mmu_page_role role);
hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
void kvm_tdp_mmu_put_root_hpa(struct kvm *kvm, hpa_t root_hpa);

--
2.28.0.709.gb0816b6eb0-goog
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