KVM: guest_memfd: Allow mmap() on guest_memfd for x86 VMs with private memory

Allow mmap() on guest_memfd instances for x86 VMs with private memory as
the need to track private vs. shared state in the guest_memfd instance is
only pertinent to INIT_SHARED.  Doing mmap() on private memory isn't
terrible useful (yet!), but it's now possible, and will be desirable when
guest_memfd gains support for other VMA-based syscalls, e.g. mbind() to
set NUMA policy.

Lift the restriction now, before MMAP support is officially released, so
that KVM doesn't need to add another capability to enumerate support for
mmap() on private memory.

Fixes: 3d3a04fad25a ("KVM: Allow and advertise support for host mmap() on guest_memfd files")
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20251003232606.4070510-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 1 insertions, 5 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5f644ca54af3..b7a0ae2a7b20 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4929,11 +4929,7 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	case KVM_CAP_GUEST_MEMFD:
 		return 1;
 	case KVM_CAP_GUEST_MEMFD_FLAGS:
-		if (!kvm || kvm_arch_supports_gmem_mmap(kvm))
-			return GUEST_MEMFD_FLAG_MMAP |
-			       GUEST_MEMFD_FLAG_INIT_SHARED;
-
-		return 0;
+		return kvm_gmem_get_supported_flags(kvm);
 #endif
 	default:
 		break;