[PATCH] hostmem: Round up memory size for qemu_madvise() in host_memory_backend_memory_complete()

[Michal Privoznik]

Simple reproducer:
qemu.git $ ./build/qemu-system-x86_64 \
-m size=8389632k,slots=16,maxmem=25600000k \
-object 
'{"qom-type":"memory-backend-file","id":"ram-node0","mem-path":"/hugepages2M/","prealloc":true,"size":8590983168,"host-nodes":[0],"policy":"bind"}'
 \
-numa node,nodeid=0,cpus=0,memdev=ram-node0

With current master I get:

qemu-system-x86_64: cannot bind memory to host NUMA nodes: Invalid argument

The problem is that memory size (8193MiB) is not an integer
multiple of underlying pagesize (2MiB) which triggers a check
inside of madvise(), since we can't really set a madvise() policy
just to a fraction of a page.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
---
 backends/hostmem.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index 747e7838c0..4e88d048de 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -326,9 +326,10 @@ host_memory_backend_memory_complete(UserCreatable *uc, 
Error **errp)
     HostMemoryBackendClass *bc = MEMORY_BACKEND_GET_CLASS(uc);
     Error *local_err = NULL;
     void *ptr;
-    uint64_t sz;
 
     if (bc->alloc) {
+        uint64_t sz;
+
         bc->alloc(backend, &local_err);
         if (local_err) {
             goto out;
@@ -337,6 +338,11 @@ host_memory_backend_memory_complete(UserCreatable *uc, 
Error **errp)
         ptr = memory_region_get_ram_ptr(&backend->mr);
         sz = memory_region_size(&backend->mr);
 
+        /* Round up size to be an integer multiple of pagesize, because
+         * madvise() does not really like setting advices on a fraction of a
+         * page. */
+        sz = ROUND_UP(sz, qemu_ram_pagesize(backend->mr.ram_block));
+
         if (backend->merge) {
             qemu_madvise(ptr, sz, QEMU_MADV_MERGEABLE);
         }
-- 
2.41.0