Current QEMU unconditionally sets the guest_memfd_offset of KVMSlot in
kvm_set_phys_mem(), which leads to the trace of kvm_set_user_memory looks:

kvm_set_user_memory AddrSpace#0 Slot#4 flags=0x2 gpa=0xe0000 size=0x20000 ua=0x7f5840de0000 guest_memfd=-1 guest_memfd_offset=0x3e0000 ret=0

It's confusing that the guest_memfd_offset has a non-zero value while
the guest_memfd is invalid (-1).

Change to only set guest_memfd_offset when guest_memfd is valid and
leave it as 0 when no valid guest_memfd.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
Changes in v2:
- initialize guest_memfd_offset in kvm_set_phys_mem(); (Phillippe)
---
 accel/kvm/kvm-all.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 90f3b177a1ff..cc694fe3c3a9 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1595,7 +1595,8 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
         mem->ram = ram;
         mem->flags = kvm_mem_flags(mr);
         mem->guest_memfd = mr->ram_block->guest_memfd;
-        mem->guest_memfd_offset = (uint8_t*)ram - mr->ram_block->host;
+        mem->guest_memfd_offset = mem->guest_memfd >= 0 ?
+                                  (uint8_t*)ram - mr->ram_block->host : 0;
 
         kvm_slot_init_dirty_bitmap(mem);
         err = kvm_set_user_memory_region(kml, mem, true);
-- 
2.43.0