[PATCH Part2 v5 21/45] KVM: SVM: Make AVIC backing, VMSA and VMCB memory allocation SNP safe
From: Brijesh Singh
Date: Fri Aug 20 2021 - 12:04:43 EST
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>
---
arch/x86/include/asm/kvm-x86-ops.h | 1 +
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/lapic.c | 5 ++++-
arch/x86/kvm/svm/sev.c | 35 ++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 16 ++++++++++++--
arch/x86/kvm/svm/svm.h | 1 +
6 files changed, 56 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index a12a4987154e..36a9c23a4b27 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -122,6 +122,7 @@ KVM_X86_OP_NULL(enable_direct_tlbflush)
KVM_X86_OP_NULL(migrate_timers)
KVM_X86_OP(msr_filter_changed)
KVM_X86_OP_NULL(complete_emulated_msr)
+KVM_X86_OP(alloc_apic_backing_page)
#undef KVM_X86_OP
#undef KVM_X86_OP_NULL
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 974cbfb1eefe..5ad6255ff5d5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1453,6 +1453,7 @@ struct kvm_x86_ops {
int (*complete_emulated_msr)(struct kvm_vcpu *vcpu, int err);
void (*vcpu_deliver_sipi_vector)(struct kvm_vcpu *vcpu, u8 vector);
+ 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 ba5a27879f1d..05b45747b20b 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2457,7 +2457,10 @@ 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 1644da5fc93f..8771b878193f 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2703,3 +2703,38 @@ 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_to_phys(pfn), PMD_SIZE)) {
+ pfn++;
+ __free_page(p);
+ } else {
+ __free_page(pfn_to_page(pfn + 1));
+ }
+
+ return pfn_to_page(pfn);
+}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 25773bf72158..058eea8353c9 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1368,7 +1368,7 @@ static int svm_create_vcpu(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;
@@ -1377,7 +1377,7 @@ static int svm_create_vcpu(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;
@@ -4539,6 +4539,16 @@ 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 = {
.hardware_unsetup = svm_hardware_teardown,
.hardware_enable = svm_hardware_enable,
@@ -4667,6 +4677,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.complete_emulated_msr = svm_complete_emulated_msr,
.vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
+
+ .alloc_apic_backing_page = svm_alloc_apic_backing_page,
};
static struct kvm_x86_init_ops svm_init_ops __initdata = {
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index d1f1512a4b47..e40800e9c998 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -575,6 +575,7 @@ void sev_es_create_vcpu(struct vcpu_svm *svm);
void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
void sev_es_prepare_guest_switch(struct vcpu_svm *svm, unsigned int cpu);
void sev_es_unmap_ghcb(struct vcpu_svm *svm);
+struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu);
/* vmenter.S */
--
2.17.1