Merge tag 'kvm-x86-fixes-6.19-rc1' of https://github.com/kvm-x86/linux into HEAD

KVM fixes for 6.19-rc1

 - Add a missing "break" to fix param parsing in the rseq selftest.

 - Apply runtime updates to the _current_ CPUID when userspace is setting
   CPUID, e.g. as part of vCPU hotplug, to fix a false positive and to avoid
   dropping the pending update.

 - Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot, as it's not
   supported by KVM and leads to a use-after-free due to KVM failing to unbind
   the memslot from the previously-associated guest_memfd instance.

 - Harden against similar KVM_MEM_GUEST_MEMFD goofs, and prepare for supporting
   flags-only changes on KVM_MEM_GUEST_MEMFD memlslots, e.g. for dirty logging.

 - Set exit_code[63:32] to -1 (all 0xffs) when synthesizing a nested
   SVM_EXIT_ERR (a.k.a. VMEXIT_INVALID) #VMEXIT, as VMEXIT_INVALID is defined
   as -1ull (a 64-bit value).

 - Update SVI when activating APICv to fix a bug where a post-activation EOI
   for an in-service IRQ would effective be lost due to SVI being stale.

 - Immediately refresh APICv controls (if necessary) on a nested VM-Exit
   instead of deferring the update via KVM_REQ_APICV_UPDATE, as the request is
   effectively ignored because KVM thinks the vCPU already has the correct
   APICv settings.

1 files changed, 16 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5fcd401a5897..5b5b69c97665 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1749,6 +1749,12 @@ static void kvm_commit_memory_region(struct kvm *kvm,
 		kvm_free_memslot(kvm, old);
 		break;
 	case KVM_MR_MOVE:
+		/*
+		 * Moving a guest_memfd memslot isn't supported, and will never
+		 * be supported.
+		 */
+		WARN_ON_ONCE(old->flags & KVM_MEM_GUEST_MEMFD);
+		fallthrough;
 	case KVM_MR_FLAGS_ONLY:
 		/*
 		 * Free the dirty bitmap as needed; the below check encompasses
@@ -1758,6 +1764,15 @@ static void kvm_commit_memory_region(struct kvm *kvm,
 			kvm_destroy_dirty_bitmap(old);
 
 		/*
+		 * Unbind the guest_memfd instance as needed; the @new slot has
+		 * already created its own binding.  TODO: Drop the WARN when
+		 * dirty logging guest_memfd memslots is supported.  Until then,
+		 * flags-only changes on guest_memfd slots should be impossible.
+		 */
+		if (WARN_ON_ONCE(old->flags & KVM_MEM_GUEST_MEMFD))
+			kvm_gmem_unbind(old);
+
+		/*
 		 * The final quirk.  Free the detached, old slot, but only its
 		 * memory, not any metadata.  Metadata, including arch specific
 		 * data, may be reused by @new.
@@ -2086,7 +2101,7 @@ static int kvm_set_memory_region(struct kvm *kvm,
 			return -EINVAL;
 		if ((mem->userspace_addr != old->userspace_addr) ||
 		    (npages != old->npages) ||
-		    ((mem->flags ^ old->flags) & KVM_MEM_READONLY))
+		    ((mem->flags ^ old->flags) & (KVM_MEM_READONLY | KVM_MEM_GUEST_MEMFD)))
 			return -EINVAL;
 
 		if (base_gfn != old->base_gfn)