[RFC PATCH 3/3] KVM: arm64: Allow dirty page logging for guest_memfd-only memslots

[Alexandru Elisei]

Everything is in place to allow dirty page logging for guest_memfd-only
memslots, advertise it to userspace.

Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
---
 arch/arm64/kvm/arm.c | 22 ++++++++++++++++++++++
 arch/arm64/kvm/mmu.c |  3 ++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 50adfff75be8..e92e5d7b533a 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -393,6 +393,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_COUNTER_OFFSET:
 	case KVM_CAP_ARM_WRITABLE_IMP_ID_REGS:
 	case KVM_CAP_ARM_SEA_TO_USER:
+#ifdef CONFIG_KVM_GUEST_MEMFD
+	case KVM_CAP_GUEST_MEMFD_MMAP_LOG_DIRTY_PAGES:
+#endif
 		r = 1;
 		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
@@ -493,6 +496,25 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	return r;
 }
 
+#ifdef CONFIG_KVM_GUEST_MEMFD
+bool kvm_arch_supports_gmem_mmap_dirty_logging(struct kvm *kvm)
+{
+	/*
+	 * Protected pKVM VMs don't allow dirty page logging, fail early here
+	 * instead of in kvm_arch_prepare_memory_region().
+	 *
+	 * KVM_CAP_GUEST_MEMFD_MMAP_LOG_DIRTY_PAGES is not available for a
+	 * protected pKVM VM, and returning false means that
+	 * KVM_SET_USER_MEMORY_REGION2 fails with EINVAL, which is consistent
+	 * with unsupported memslot flags.
+	 */
+	if (!is_protected_kvm_enabled())
+		return true;
+
+	return kvm_pkvm_ext_allowed(kvm, KVM_CAP_GUEST_MEMFD_MMAP_LOG_DIRTY_PAGES);
+}
+#endif
+
 long kvm_arch_dev_ioctl(struct file *filp,
 			unsigned int ioctl, unsigned long arg)
 {
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 6c941aaa10c6..f6e6de153ce2 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1648,7 +1648,8 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 		return ret;
 	}
 
-	if (!(s2fd->memslot->flags & KVM_MEM_READONLY))
+	if (!(s2fd->memslot->flags & KVM_MEM_READONLY) &&
+	    (!kvm_slot_dirty_track_enabled(s2fd->memslot) || write_fault))
 		prot |= KVM_PGTABLE_PROT_W;
 
 	if (s2fd->nested)
-- 
2.43.0