[PATCH v3 17/19] accel/kvm: Disable discard for in-place conversion

[Michael Roth <michael.roth@amd.com>]

When using in-place conversion, there is no need to discard memory after
conversion because the same memory will continue to be used after the
conversion to back the same GPA. Discarding it would only cause
unnecessary reallocation of memory after each conversion. Instead, only
enable it for non-in-place conversions.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index bfb8b4a190..dfcfb3b5cc 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3588,7 +3588,7 @@ static int kvm_post_convert_section(MemoryRegionSection *section, bool to_privat
     ram_addr_t offset;
     RAMBlock *rb;
     void *addr;
-    int ret;
+    int ret = 0;
 
     addr = memory_region_get_ram_ptr(mr) + section->offset_within_region;
     rb = qemu_ram_block_from_host(addr, false, &offset);
@@ -3611,17 +3611,19 @@ static int kvm_post_convert_section(MemoryRegionSection *section, bool to_privat
         }
     }
 
-    if (to_private) {
-        if (rb->page_size != qemu_real_host_page_size()) {
-            /*
-             * shared memory is backed by hugetlb, which is supposed to be
-             * pre-allocated and doesn't need to be discarded
-             */
-            return 0;
+    if (!machine_require_guest_memfd_convert_in_place(current_machine)) {
+        if (to_private) {
+            if (rb->page_size != qemu_real_host_page_size()) {
+                /*
+                 * shared memory is backed by hugetlb, which is supposed to be
+                 * pre-allocated and doesn't need to be discarded
+                 */
+                return 0;
+            }
+            ret = ram_block_discard_shared_range(rb, offset, size);
+        } else {
+            ret = ram_block_discard_guest_memfd_range(rb, offset, size);
         }
-        ret = ram_block_discard_shared_range(rb, offset, size);
-    } else {
-        ret = ram_block_discard_guest_memfd_range(rb, offset, size);
     }
 
     return ret;
-- 
2.43.0