[PATCH 21/22] kvm: x86/mmu: Don't clear write flooding count for direct roots

[Paolo Bonzini]

From: Ben Gardon <bgardon@xxxxxxxxxx>

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@xxxxxxxxxx>
Message-Id: <20201014182700.2888246-20-bgardon@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 6a0941ccac34..7b52fa1f01b0 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3892,7 +3892,13 @@ 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,
-- 
2.26.2