KVM: x86/mmu: Alloc page for PDPTEs when shadowing 32-bit NPT with 64-bit

Allocate the so called pae_root page on-demand, along with the lm_root
page, when shadowing 32-bit NPT with 64-bit NPT, i.e. when running a
32-bit L1.  KVM currently only allocates the page when NPT is disabled,
or when L0 is 32-bit (using PAE paging).

Note, there is an existing memory leak involving the MMU roots, as KVM
fails to free the PAE roots on failure.  This will be addressed in a
future commit.

Fixes: ee6268ba3a68 ("KVM: x86: Skip pae_root shadow allocation if tdp enabled")
Fixes: b6b80c78af83 ("KVM: x86/mmu: Allocate PAE root array when using SVM's 32-bit NPT")
Cc: stable@vger.kernel.org
Reviewed-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210305011101.3597423-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d75524b..b52bd62 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3193,14 +3193,14 @@ void kvm_mmu_free_roots(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
                if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL &&
                    (mmu->root_level >= PT64_ROOT_4LEVEL || mmu->direct_map)) {
                        mmu_free_root_page(kvm, &mmu->root_hpa, &invalid_list);
-               } else {
+               } 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);
-                       mmu->root_hpa = INVALID_PAGE;
                }
+               mmu->root_hpa = INVALID_PAGE;
                mmu->root_pgd = 0;
        }
 
@@ -3312,9 +3312,23 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
         * the shadow page table may be a PAE or a long mode page table.
         */
        pm_mask = PT_PRESENT_MASK;
-       if (vcpu->arch.mmu->shadow_root_level == PT64_ROOT_4LEVEL)
+       if (vcpu->arch.mmu->shadow_root_level == PT64_ROOT_4LEVEL) {
                pm_mask |= PT_ACCESSED_MASK | PT_WRITABLE_MASK | PT_USER_MASK;
 
+               /*
+                * Allocate the page for the PDPTEs when shadowing 32-bit NPT
+                * with 64-bit only when needed.  Unlike 32-bit NPT, it doesn't
+                * need to be in low mem.  See also lm_root below.
+                */
+               if (!vcpu->arch.mmu->pae_root) {
+                       WARN_ON_ONCE(!tdp_enabled);
+
+                       vcpu->arch.mmu->pae_root = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
+                       if (!vcpu->arch.mmu->pae_root)
+                               return -ENOMEM;
+               }
+       }
+
        for (i = 0; i < 4; ++i) {
                MMU_WARN_ON(VALID_PAGE(vcpu->arch.mmu->pae_root[i]));
                if (vcpu->arch.mmu->root_level == PT32E_ROOT_LEVEL) {
@@ -3337,21 +3351,19 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
        vcpu->arch.mmu->root_hpa = __pa(vcpu->arch.mmu->pae_root);
 
        /*
-        * If we shadow a 32 bit page table with a long mode page
-        * table we enter this path.
+        * When shadowing 32-bit or PAE NPT with 64-bit NPT, the PML4 and PDP
+        * tables are allocated and initialized at MMU creation as there is no
+        * equivalent level in the guest's NPT to shadow.  Allocate the tables
+        * on demand, as running a 32-bit L1 VMM is very rare.  The PDP is
+        * handled above (to share logic with PAE), deal with the PML4 here.
         */
        if (vcpu->arch.mmu->shadow_root_level == PT64_ROOT_4LEVEL) {
                if (vcpu->arch.mmu->lm_root == NULL) {
-                       /*
-                        * The additional page necessary for this is only
-                        * allocated on demand.
-                        */
-
                        u64 *lm_root;
 
                        lm_root = (void*)get_zeroed_page(GFP_KERNEL_ACCOUNT);
-                       if (lm_root == NULL)
-                               return 1;
+                       if (!lm_root)
+                               return -ENOMEM;
 
                        lm_root[0] = __pa(vcpu->arch.mmu->pae_root) | pm_mask;
 
@@ -5240,9 +5252,11 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
         * while the PDP table is a per-vCPU construct that's allocated at MMU
         * creation.  When emulating 32-bit mode, cr3 is only 32 bits even on
         * x86_64.  Therefore we need to allocate the PDP table in the first
-        * 4GB of memory, which happens to fit the DMA32 zone.  Except for
-        * SVM's 32-bit NPT support, TDP paging doesn't use PAE paging and can
-        * skip allocating the PDP table.
+        * 4GB of memory, which happens to fit the DMA32 zone.  TDP paging
+        * generally doesn't use PAE paging and can skip allocating the PDP
+        * table.  The main exception, handled here, is SVM's 32-bit NPT.  The
+        * other exception is for shadowing L1's 32-bit or PAE NPT on 64-bit
+        * KVM; that horror is handled on-demand by mmu_alloc_shadow_roots().
         */
        if (tdp_enabled && kvm_mmu_get_tdp_level(vcpu) > PT32E_ROOT_LEVEL)
                return 0;