[PATCH v3 15/49] kvm/memory: Make memory type private by default if it has guest memfd backend

[Michael Roth <michael.roth@xxxxxxx>]

From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>

KVM side leaves the memory to shared by default, while may incur the
overhead of paging conversion on the first visit of each page. Because
the expectation is that page is likely to private for the VMs that
require private memory (has guest memfd).

Explicitly set the memory to private when memory region has valid
guest memfd backend.

Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
 accel/kvm/kvm-all.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 9a8b365a69..53ce4f091e 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -1451,6 +1451,16 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
                     strerror(-err));
             abort();
         }
+
+        if (memory_region_has_guest_memfd(mr)) {
+            err = kvm_set_memory_attributes_private(start_addr, slot_size);
+            if (err) {
+                error_report("%s: failed to set memory attribute private: %s\n",
+                             __func__, strerror(-err));
+                exit(1);
+            }
+        }
+
         start_addr += slot_size;
         ram_start_offset += slot_size;
         ram += slot_size;
-- 
2.25.1