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 4a98623d5d90175c0f99d185171e60807391e487 Mon Sep 17 00:00:00 2001
From: Sean Christopherson seanjc@google.com Date: Tue, 9 Mar 2021 14:42:07 -0800 Subject: [PATCH] KVM: x86/mmu: Mark the PAE roots as decrypted for shadow paging
Set the PAE roots used as decrypted to play nice with SME when KVM is using shadow paging. Explicitly skip setting the C-bit when loading CR3 for PAE shadow paging, even though it's completely ignored by the CPU. The extra documentation is nice to have.
Note, there are several subtleties at play with NPT. In addition to legacy shadow paging, the PAE roots are used for SVM's NPT when either KVM is 32-bit (uses PAE paging) or KVM is 64-bit and shadowing 32-bit NPT. However, 32-bit Linux, and thus KVM, doesn't support SME. And 64-bit KVM can happily set the C-bit in CR3. This also means that keeping __sme_set(root) for 32-bit KVM when NPT is enabled is conceptually wrong, but functionally ok since SME is 64-bit only. Leave it as is to avoid unnecessary pollution.
Fixes: d0ec49d4de90 ("kvm/x86/svm: Support Secure Memory Encryption within KVM") Cc: stable@vger.kernel.org Cc: Brijesh Singh brijesh.singh@amd.com Cc: Tom Lendacky thomas.lendacky@amd.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20210309224207.1218275-5-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 6b0576ff2846..c6ed633594a2 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -48,6 +48,7 @@ #include <asm/memtype.h> #include <asm/cmpxchg.h> #include <asm/io.h> +#include <asm/set_memory.h> #include <asm/vmx.h> #include <asm/kvm_page_track.h> #include "trace.h" @@ -3388,7 +3389,10 @@ static int mmu_alloc_special_roots(struct kvm_vcpu *vcpu) if (WARN_ON_ONCE(!tdp_enabled || mmu->pae_root || mmu->lm_root)) return -EIO;
- /* Unlike 32-bit NPT, the PDP table doesn't need to be in low mem. */ + /* + * Unlike 32-bit NPT, the PDP table doesn't need to be in low mem, and + * doesn't need to be decrypted. + */ pae_root = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT); if (!pae_root) return -ENOMEM; @@ -5274,6 +5278,8 @@ slot_handle_leaf(struct kvm *kvm, struct kvm_memory_slot *memslot,
static void free_mmu_pages(struct kvm_mmu *mmu) { + if (!tdp_enabled && mmu->pae_root) + set_memory_encrypted((unsigned long)mmu->pae_root, 1); free_page((unsigned long)mmu->pae_root); free_page((unsigned long)mmu->lm_root); } @@ -5308,6 +5314,20 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) return -ENOMEM;
mmu->pae_root = page_address(page); + + /* + * CR3 is only 32 bits when PAE paging is used, thus it's impossible to + * get the CPU to treat the PDPTEs as encrypted. Decrypt the page so + * that KVM's writes and the CPU's reads get along. Note, this is + * only necessary when using shadow paging, as 64-bit NPT can get at + * the C-bit even when shadowing 32-bit NPT, and SME isn't supported + * by 32-bit kernels (when KVM itself uses 32-bit NPT). + */ + if (!tdp_enabled) + set_memory_decrypted((unsigned long)mmu->pae_root, 1); + else + WARN_ON_ONCE(shadow_me_mask); + for (i = 0; i < 4; ++i) mmu->pae_root[i] = INVALID_PAE_ROOT;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 58f4dc0e7864..271196400495 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3907,9 +3907,8 @@ static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, struct vcpu_svm *svm = to_svm(vcpu); unsigned long cr3;
- root_hpa = __sme_set(root_hpa); if (npt_enabled) { - svm->vmcb->control.nested_cr3 = root_hpa; + svm->vmcb->control.nested_cr3 = __sme_set(root_hpa); vmcb_mark_dirty(svm->vmcb, VMCB_NPT);
/* Loading L2's CR3 is handled by enter_svm_guest_mode. */ @@ -3917,7 +3916,7 @@ static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa, return; cr3 = vcpu->arch.cr3; } else if (vcpu->arch.mmu->shadow_root_level >= PT64_ROOT_4LEVEL) { - cr3 = root_hpa | kvm_get_active_pcid(vcpu); + cr3 = __sme_set(root_hpa) | kvm_get_active_pcid(vcpu); } else { /* PCID in the guest should be impossible with a 32-bit MMU. */ WARN_ON_ONCE(kvm_get_active_pcid(vcpu));