[PATCH 6/8] kvm/x86: Add mem fault exit on EPT violations

[Anish Moorthy <amoorthy@xxxxxxxxxx>]

With the relevant kvm cap enabled, EPT violations will exit to userspace
w/ reason KVM_EXIT_MEMORY_FAULT instead of resolving the fault via slow
get_user_pages.

Signed-off-by: Anish Moorthy <amoorthy@xxxxxxxxxx>
Suggested-by: James Houghton <jthoughton@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c | 23 ++++++++++++++++++++---
 arch/x86/kvm/x86.c     |  1 +
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index aeb240b339f54..28af8d60adee6 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4201,6 +4201,7 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 {
 	struct kvm_memory_slot *slot = fault->slot;
 	bool async;
+	bool mem_fault_nowait;
 
 	/*
 	 * Retry the page fault if the gfn hit a memslot that is being deleted
@@ -4230,9 +4231,25 @@ 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);
+	mem_fault_nowait = memory_faults_enabled(vcpu->kvm);
+
+	fault->pfn = __gfn_to_pfn_memslot(
+		slot, fault->gfn,
+		mem_fault_nowait,
+		false,
+		mem_fault_nowait ? NULL : &async,
+		fault->write, &fault->map_writable,
+		&fault->hva);
+
+	if (mem_fault_nowait) {
+		if (fault->pfn == KVM_PFN_ERR_FAULT) {
+			vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
+			vcpu->run->memory_fault.gpa = fault->gfn << PAGE_SHIFT;
+			vcpu->run->memory_fault.size = PAGE_SIZE;
+		}
+		return RET_PF_CONTINUE;
+	}
+
 	if (!async)
 		return RET_PF_CONTINUE; /* *pfn has correct page already */
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 508074e47bc0e..fe39ab2af5db4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4427,6 +4427,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_VAPIC:
 	case KVM_CAP_ENABLE_CAP:
 	case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES:
+	case KVM_CAP_MEM_FAULT_NOWAIT:
 		r = 1;
 		break;
 	case KVM_CAP_EXIT_HYPERCALL:
-- 
2.39.1.581.gbfd45094c4-goog