diff mbox series

[v3,18/22] KVM: x86: Implement KVM_CAP_ABSENT_MAPPING_FAULT

Message ID 20230412213510.1220557-19-amoorthy@google.com (mailing list archive)
State New, archived
Headers show
Series Improve scalability of KVM + userfaultfd live migration via annotated memory faults. | expand

Commit Message

Anish Moorthy April 12, 2023, 9:35 p.m. UTC 
When the memslot flag is enabled, fail guest memory accesses for which
fast-gup fails (ie, for which the mappings are not present).

Suggested-by: James Houghton <jthoughton@google.com>
Signed-off-by: Anish Moorthy <amoorthy@google.com>
---
 Documentation/virt/kvm/api.rst |  2 +-
 arch/x86/kvm/mmu/mmu.c         | 17 ++++++++++++-----
 arch/x86/kvm/x86.c             |  1 +
 3 files changed, 14 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 7967b9909e28b..452bbca800b15 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7712,7 +7712,7 @@  reported to the maintainers.
 7.35 KVM_CAP_ABSENT_MAPPING_FAULT
 ---------------------------------
 
-:Architectures: None
+:Architectures: x86
 :Returns: -EINVAL.
 
 The presence of this capability indicates that userspace may pass the
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d83a3e1e3eff9..4aef79b97c985 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4218,7 +4218,9 @@  void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
 	kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true, NULL);
 }
 
-static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
+static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu,
+				struct kvm_page_fault *fault,
+				bool fault_on_absent_mapping)
 {
 	struct kvm_memory_slot *slot = fault->slot;
 	bool async;
@@ -4251,9 +4253,12 @@  static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 	}
 
 	async = false;
-	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
-					  fault->write, &fault->map_writable,
-					  &fault->hva);
+
+	fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn,
+						fault_on_absent_mapping, false,
+						fault_on_absent_mapping ? NULL : &async,
+						fault->write, &fault->map_writable, &fault->hva);
+
 	if (!async)
 		return RET_PF_CONTINUE; /* *pfn has correct page already */
 
@@ -4287,7 +4292,9 @@  static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq;
 	smp_rmb();
 
-	ret = __kvm_faultin_pfn(vcpu, fault);
+	ret = __kvm_faultin_pfn(vcpu, fault,
+				likely(fault->slot)
+					&& kvm_slot_fault_on_absent_mapping(fault->slot));
 	if (ret != RET_PF_CONTINUE)
 		return ret;
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3e9deab31e1c8..bc465cde7acf6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4433,6 +4433,7 @@  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ENABLE_CAP:
 	case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES:
 	case KVM_CAP_MEMORY_FAULT_INFO:
+	case KVM_CAP_ABSENT_MAPPING_FAULT:
 		r = 1;
 		break;
 	case KVM_CAP_EXIT_HYPERCALL: