From: Brijesh Singh <brijesh.singh@xxxxxxx> Implement a workaround for an SNP erratum where the CPU will incorrectly signal an RMP violation #PF if a hugepage (2mb or 1gb) collides with the RMP entry of a VMCB, VMSA or AVIC backing page. When SEV-SNP is globally enabled, the CPU marks the VMCB, VMSA, and AVIC backing pages as "in-use" in the RMP after a successful VMRUN. This is done for _all_ VMs, not just SNP-Active VMs. If the hypervisor accesses an in-use page through a writable translation, the CPU will throw an RMP violation #PF. On early SNP hardware, if an in-use page is 2mb aligned and software accesses any part of the associated 2mb region with a hupage, the CPU will incorrectly treat the entire 2mb region as in-use and signal a spurious RMP violation #PF. The recommended is to not use the hugepage for the VMCB, VMSA or AVIC backing page. Add a generic allocator that will ensure that the page returns is not hugepage (2mb or 1gb) and is safe to be used when SEV-SNP is enabled. Co-developed-by: Marc Orr <marcorr@xxxxxxxxxx> Signed-off-by: Marc Orr <marcorr@xxxxxxxxxx> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx> Signed-off-by: Michael Roth <michael.roth@xxxxxxx> --- arch/x86/include/asm/kvm-x86-ops.h | 1 + arch/x86/include/asm/kvm_host.h | 2 ++ arch/x86/kvm/lapic.c | 5 ++++- arch/x86/kvm/svm/sev.c | 33 ++++++++++++++++++++++++++++++ arch/x86/kvm/svm/svm.c | 15 ++++++++++++-- arch/x86/kvm/svm/svm.h | 1 + 6 files changed, 54 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h index 6a885f024a00..e116405cbb5f 100644 --- a/arch/x86/include/asm/kvm-x86-ops.h +++ b/arch/x86/include/asm/kvm-x86-ops.h @@ -131,6 +131,7 @@ KVM_X86_OP(msr_filter_changed) KVM_X86_OP(complete_emulated_msr) KVM_X86_OP(vcpu_deliver_sipi_vector) KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons); +KVM_X86_OP_OPTIONAL(alloc_apic_backing_page) KVM_X86_OP_OPTIONAL_RET0(fault_is_private); KVM_X86_OP_OPTIONAL_RET0(update_mem_attr) KVM_X86_OP_OPTIONAL(invalidate_restricted_mem) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 37c92412035f..a9363a6f779d 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1729,6 +1729,8 @@ struct kvm_x86_ops { * Returns vCPU specific APICv inhibit reasons */ unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu); + + void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu); }; struct kvm_x86_nested_ops { diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 80f92cbc4029..72e46d5b4201 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -2740,7 +2740,10 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns) vcpu->arch.apic = apic; - apic->regs = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT); + if (kvm_x86_ops.alloc_apic_backing_page) + apic->regs = static_call(kvm_x86_alloc_apic_backing_page)(vcpu); + else + apic->regs = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT); if (!apic->regs) { printk(KERN_ERR "malloc apic regs error for vcpu %x\n", vcpu->vcpu_id); diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index c1f0d4898ce3..9e9efb42a766 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -3241,3 +3241,36 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector) break; } } + +struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu) +{ + unsigned long pfn; + struct page *p; + + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP)) + return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); + + /* + * Allocate an SNP safe page to workaround the SNP erratum where + * the CPU will incorrectly signal an RMP violation #PF if a + * hugepage (2mb or 1gb) collides with the RMP entry of VMCB, VMSA + * or AVIC backing page. The recommeded workaround is to not use the + * hugepage. + * + * Allocate one extra page, use a page which is not 2mb aligned + * and free the other. + */ + p = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_ZERO, 1); + if (!p) + return NULL; + + split_page(p, 1); + + pfn = page_to_pfn(p); + if (IS_ALIGNED(pfn, PTRS_PER_PMD)) + __free_page(p++); + else + __free_page(p + 1); + + return p; +} diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 213593dbd7a1..1061aaf66f0a 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1372,7 +1372,7 @@ static int svm_vcpu_create(struct kvm_vcpu *vcpu) svm = to_svm(vcpu); err = -ENOMEM; - vmcb01_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); + vmcb01_page = snp_safe_alloc_page(vcpu); if (!vmcb01_page) goto out; @@ -1381,7 +1381,7 @@ static int svm_vcpu_create(struct kvm_vcpu *vcpu) * SEV-ES guests require a separate VMSA page used to contain * the encrypted register state of the guest. */ - vmsa_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO); + vmsa_page = snp_safe_alloc_page(vcpu); if (!vmsa_page) goto error_free_vmcb_page; @@ -4696,6 +4696,16 @@ static int svm_vm_init(struct kvm *kvm) return 0; } +static void *svm_alloc_apic_backing_page(struct kvm_vcpu *vcpu) +{ + struct page *page = snp_safe_alloc_page(vcpu); + + if (!page) + return NULL; + + return page_address(page); +} + static struct kvm_x86_ops svm_x86_ops __initdata = { .name = KBUILD_MODNAME, @@ -4824,6 +4834,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = { .vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector, .vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons, + .alloc_apic_backing_page = svm_alloc_apic_backing_page, }; /* diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index c249c360fe36..5efcf036ccad 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -692,6 +692,7 @@ void sev_es_vcpu_reset(struct vcpu_svm *svm); void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector); void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa); void sev_es_unmap_ghcb(struct vcpu_svm *svm); +struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu); /* vmenter.S */ -- 2.25.1