On 10/24/2025 2:59 AM, Peter Xu wrote:
> 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.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> accel/kvm/kvm-all.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 1425dfd8b3..48a8f6424f 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -108,6 +108,7 @@ static int kvm_sstep_flags;
> 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_capabilites[] = {
> @@ -2781,6 +2782,11 @@ static int kvm_init(AccelState *as, MachineState *ms)
> kvm_supported_memory_attributes = kvm_vm_check_extension(s, KVM_CAP_MEMORY_ATTRIBUTES);
> kvm_guest_memfd_supported = kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
> kvm_vm_check_extension(s, KVM_CAP_USER_MEMORY2);
> + ret = kvm_vm_check_extension(s, KVM_CAP_GUEST_MEMFD_FLAGS);
> + if (ret > 0)
> + kvm_guest_memfd_flags_supported = (uint64_t)ret;
> + else
> + kvm_guest_memfd_flags_supported = 0;
Nit:
1. QEMU's coding style always requires curly braces.
2. is the (uint64_t) necessary?
3. can we name it "kvm_supported_guest_memfd_flags" to make it
consistent with "kvm_supported_memory_attributes"?
so how about
kvm_supported_guest_memfd_flags = kvm_vm_check_extension(s,
KVM_CAP_GUEST_MEMFD_FLAGS);
if (kvm_supported_guest_memfd_flags < 0) {
kvm_supported_guest_memfd_flags = 0;
}
> kvm_pre_fault_memory_supported = kvm_vm_check_extension(s, KVM_CAP_PRE_FAULT_MEMORY);
>
> if (s->kernel_irqchip_split == ON_OFF_AUTO_AUTO) {
> @@ -4486,6 +4492,12 @@ 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, "KVM 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");