[Qemu-devel] [PATCH 2/2] postcopy: Require RAMBlocks that are whole pages

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

It turns out that it's legal to create a VM with RAMBlocks that aren't
a multiple of the pagesize in use; e.g. a 1025M main memory using
2M host pages.  That breaks postcopy's atomic placement of pages,
so disallow it.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/postcopy-ram.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index cdadaf6578..e8f43e7bd1 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -96,14 +96,24 @@ static bool ufd_version_check(int ufd)
 
 /* Callback from postcopy_ram_supported_by_host block iterator.
  */
-static int test_range_shared(const char *block_name, void *host_addr,
+static int test_ramblock_postcopiable(const char *block_name, void *host_addr,
                              ram_addr_t offset, ram_addr_t length, void *opaque)
 {
-    if (qemu_ram_is_shared(qemu_ram_block_by_name(block_name))) {
+    RAMBlock *rb = qemu_ram_block_by_name(block_name);
+    size_t pagesize = qemu_ram_pagesize(rb);
+
+    if (qemu_ram_is_shared(rb)) {
         error_report("Postcopy on shared RAM (%s) is not yet supported",
                      block_name);
         return 1;
     }
+
+    if (length % pagesize) {
+        error_report("Postcopy requires RAM blocks to be a page size multiple,"
+                     " block %s is 0x" RAM_ADDR_FMT " bytes with a "
+                     "page size of 0x%zx", block_name, length, pagesize);
+        return 1;
+    }
     return 0;
 }
 
@@ -140,7 +150,7 @@ bool postcopy_ram_supported_by_host(void)
     }
 
     /* We don't support postcopy with shared RAM yet */
-    if (qemu_ram_foreach_block(test_range_shared, NULL)) {
+    if (qemu_ram_foreach_block(test_ramblock_postcopiable, NULL)) {
         goto out;
     }
 
-- 
2.13.0