The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 04d45551a1eefbea42655da52f56e846c0af721a Mon Sep 17 00:00:00 2001

From: Sean Christopherson seanjc@google.com Date: Thu, 4 Mar 2021 17:10:46 -0800 Subject: [PATCH] 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 d75524bc8423..b52bd620d1e5 100644 --- 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;