Commit 9a8a6bd227 for qemu.org

commit 9a8a6bd227a98b69183c698bf6129e73e2fae9b4
Author: Peter Xu <peterx@redhat.com>
Date:   Tue Sep 29 18:50:08 2026 -0500

    kvm: Detect guest-memfd flags supported

    Detect supported guest-memfd flags by the current kernel, and reject
    creations of guest-memfd using invalid flags.  When the cap isn't
    available, then no flag is supported.

    Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
    Reviewed-by: Fabiano Rosas <farosas@suse.de>
    Reviewed-by: Michael Roth <michael.roth@amd.com>
    Signed-off-by: Michael Roth <michael.roth@amd.com>
    Link: https://lore.kernel.org/r/20260929235109.1398509-3-michael.roth@amd.com
    Signed-off-by: Peter Xu <peterx@redhat.com>

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index cdc7554082..120cab1e22 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -107,6 +107,7 @@ bool kvm_pre_fault_memory_supported;
 static bool kvm_immediate_exit;
 static uint64_t kvm_supported_memory_attributes;
 static bool kvm_guest_memfd_supported;
+static uint64_t kvm_guest_memfd_flags_supported;
 static hwaddr kvm_max_slot_size = ~0;

 static const KVMCapabilityInfo kvm_required_capabilities[] = {
@@ -3065,6 +3066,8 @@ static int kvm_init(AccelState *as, MachineState *ms)
         kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
         kvm_vm_check_extension(s, KVM_CAP_USER_MEMORY2);
     kvm_pre_fault_memory_supported = kvm_vm_check_extension(s, KVM_CAP_PRE_FAULT_MEMORY);
+    kvm_guest_memfd_flags_supported =
+        kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD_FLAGS);

     if (s->kernel_irqchip_split == ON_OFF_AUTO_AUTO) {
         s->kernel_irqchip_split = mc->default_kernel_irqchip_split ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
@@ -4760,6 +4763,13 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
         return -1;
     }

+    if (flags & ~kvm_guest_memfd_flags_supported) {
+        error_setg(errp, "Current KVM instance does not support "
+                   "guest-memfd flag: 0x%"PRIx64,
+                   flags & ~kvm_guest_memfd_flags_supported);
+        return -1;
+    }
+
     fd = kvm_vm_ioctl(kvm_state, KVM_CREATE_GUEST_MEMFD, &guest_memfd);
     if (fd < 0) {
         error_setg_errno(errp, errno, "Error creating KVM guest_memfd");