linux-kernel - [PATCH 07/15] KVM: x86/mmu: Use '0' as the one and only value for an invalid PAE root

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Message-Id: <20210302184540.2829328-8-seanjc@google.com>
Date:   Tue,  2 Mar 2021 10:45:32 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 07/15] KVM: x86/mmu: Use '0' as the one and only value for an
 invalid PAE root

Use '0' to denote an invalid pae_root instead of '0' or INVALID_PAGE.
Unlike root_hpa, the pae_roots hold permission bits and thus are
guaranteed to be non-zero.  Having to deal with both values leads to
bugs, e.g. failing to set back to INVALID_PAGE, warning on the wrong
value, etc...

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3ef7fb2a9878..59b1709a55b4 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3191,11 +3191,14 @@ void kvm_mmu_free_roots(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 		    (mmu->root_level >= PT64_ROOT_4LEVEL || mmu->direct_map)) {
 			mmu_free_root_page(kvm, &mmu->root_hpa, &invalid_list);
 		} else if (mmu->pae_root) {
-			for (i = 0; i < 4; ++i)
-				if (mmu->pae_root[i] != 0)
-					mmu_free_root_page(kvm,
-							   &mmu->pae_root[i],
-							   &invalid_list);
+			for (i = 0; i < 4; ++i) {
+				if (!mmu->pae_root[i])
+					continue;
+
+				mmu_free_root_page(kvm, &mmu->pae_root[i],
+						   &invalid_list);
+				mmu->pae_root[i] = 0;
+			}
 		}
 		mmu->root_hpa = INVALID_PAGE;
 		mmu->root_pgd = 0;
@@ -3244,8 +3247,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
 		vcpu->arch.mmu->root_hpa = root;
 	} else if (shadow_root_level == PT32E_ROOT_LEVEL) {
 		for (i = 0; i < 4; ++i) {
-			WARN_ON_ONCE(vcpu->arch.mmu->pae_root[i] &&
-				     VALID_PAGE(vcpu->arch.mmu->pae_root[i]));
+			WARN_ON_ONCE(vcpu->arch.mmu->pae_root[i]);
 
 			root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT),
 					      i << 30, PT32_ROOT_LEVEL, true);
@@ -3338,8 +3340,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 	}
 
 	for (i = 0; i < 4; ++i) {
-		WARN_ON_ONCE(vcpu->arch.mmu->pae_root[i] &&
-			     VALID_PAGE(vcpu->arch.mmu->pae_root[i]));
+		WARN_ON_ONCE(vcpu->arch.mmu->pae_root[i]);
 
 		if (vcpu->arch.mmu->root_level == PT32E_ROOT_LEVEL) {
 			if (!(pdptrs[i] & PT_PRESENT_MASK)) {
@@ -3412,7 +3413,7 @@ void kvm_mmu_sync_roots(struct kvm_vcpu *vcpu)
 	for (i = 0; i < 4; ++i) {
 		hpa_t root = vcpu->arch.mmu->pae_root[i];
 
-		if (root && VALID_PAGE(root)) {
+		if (root && !WARN_ON_ONCE(!VALID_PAGE(root))) {
 			root &= PT64_BASE_ADDR_MASK;
 			sp = to_shadow_page(root);
 			mmu_sync_children(vcpu, sp);
@@ -5267,7 +5268,7 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
 
 	mmu->pae_root = page_address(page);
 	for (i = 0; i < 4; ++i)
-		mmu->pae_root[i] = INVALID_PAGE;
+		mmu->pae_root[i] = 0;
 
 	return 0;
 }
-- 
2.30.1.766.gb4fecdf3b7-goog