[RFC PATCH 3/6] KVM: guest_memfd, x86: MEMORY_FAULT exit with hw poisoned page

[isaku.yamahata@xxxxxxxxx]

From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>

When resolving kvm page fault and hwpoisoned page is given, KVM exit
with HWPOISONED flag so that user space VMM, e.g. qemu, handle it.

- Add a new flag POISON to KVM_EXIT_MEMORY_FAULT to indicate the page is
  poisoned.
- Make kvm_gmem_get_pfn() return hwpoison state by -EHWPOISON when the
  folio is hw-poisoned.
- When page is hw-poisoned on faulting in private gmem, return
  KVM_EXIT_MEMORY_FAULT with HWPOISONED flag.

Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c   | 21 +++++++++++++++------
 include/uapi/linux/kvm.h |  3 ++-
 virt/kvm/guest_mem.c     |  4 +++-
 3 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 05943ccb55a4..5dc9d1fdadca 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4335,19 +4335,24 @@ static inline u8 kvm_max_level_for_order(int order)
 	return PG_LEVEL_4K;
 }
 
-static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
-				    struct kvm_page_fault *fault)
+static int __kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
+				      struct kvm_page_fault *fault, __u64 flags)
 {
 	vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
 	if (fault->is_private)
-		vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
-	else
-		vcpu->run->memory.flags = 0;
+		flags |= KVM_MEMORY_EXIT_FLAG_PRIVATE;
+	vcpu->run->flags = flags;
 	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
 	vcpu->run->memory.size = PAGE_SIZE;
 	return RET_PF_USER;
 }
 
+static int kvm_do_memory_fault_exit(struct kvm_vcpu *vcpu,
+				    struct kvm_page_fault *fault)
+{
+	return __kvm_do_memory_fault_exit(vcpu, fault, 0);
+}
+
 static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
 				   struct kvm_page_fault *fault)
 {
@@ -4358,12 +4363,16 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
 
 	r = kvm_gmem_get_pfn(vcpu->kvm, fault->slot, fault->gfn, &fault->pfn,
 			     &max_order);
-	if (r)
+	if (r && r != -EHWPOISON)
 		return r;
 
 	fault->max_level = min(kvm_max_level_for_order(max_order),
 			       fault->max_level);
 	fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY);
+
+	if (r == -EHWPOISON)
+		return __kvm_do_memory_fault_exit(vcpu, fault,
+						  KVM_MEMORY_EXIT_FLAG_HWPOISON);
 	return RET_PF_CONTINUE;
 }
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index eb900344a054..48329cb44415 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -527,7 +527,8 @@ struct kvm_run {
 		} notify;
 		/* KVM_EXIT_MEMORY_FAULT */
 		struct {
-#define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1ULL << 3)
+#define KVM_MEMORY_EXIT_FLAG_PRIVATE	BIT_ULL(3)
+#define KVM_MEMORY_EXIT_FLAG_HWPOISON	BIT_ULL(4)
 			__u64 flags;
 			__u64 gpa;
 			__u64 size;
diff --git a/virt/kvm/guest_mem.c b/virt/kvm/guest_mem.c
index 746e683df589..3678287d7c9d 100644
--- a/virt/kvm/guest_mem.c
+++ b/virt/kvm/guest_mem.c
@@ -589,6 +589,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 {
 	pgoff_t index = gfn - slot->base_gfn + slot->gmem.pgoff;
 	struct kvm_gmem *gmem;
+	bool hwpoison = false;
 	struct folio *folio;
 	struct page *page;
 	struct file *file;
@@ -610,6 +611,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 		return -ENOMEM;
 	}
 
+	hwpoison = folio_test_hwpoison(folio);
 	page = folio_file_page(folio, index);
 
 	*pfn = page_to_pfn(page);
@@ -618,7 +620,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 	folio_unlock(folio);
 	fput(file);
 
-	return 0;
+	return hwpoison ? -EHWPOISON : 0;
 }
 EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
 
-- 
2.25.1