[PATCH v2 09/17] KVM: x86/mmu: Use '0' as the one and only value for an invalid PAE root

[Sean Christopherson]

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 <sea...@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b82c1b0d6d6e..dbf7f0395e4b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3197,11 +3197,14 @@ 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;
@@ -3250,8 +3253,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
                mmu->root_hpa = root;
        } else if (shadow_root_level == PT32E_ROOT_LEVEL) {
                for (i = 0; i < 4; ++i) {
-                       WARN_ON_ONCE(mmu->pae_root[i] &&
-                                    VALID_PAGE(mmu->pae_root[i]));
+                       WARN_ON_ONCE(mmu->pae_root[i]);
 
                        root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT),
                                              i << 30, PT32_ROOT_LEVEL, true);
@@ -3316,7 +3318,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
        }
 
        for (i = 0; i < 4; ++i) {
-               WARN_ON_ONCE(mmu->pae_root[i] && VALID_PAGE(mmu->pae_root[i]));
+               WARN_ON_ONCE(mmu->pae_root[i]);
 
                if (mmu->root_level == PT32E_ROOT_LEVEL) {
                        if (!(pdptrs[i] & PT_PRESENT_MASK)) {
@@ -3438,7 +3440,7 @@ 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);
@@ -5296,7 +5298,7 @@ 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