[PATCH 3/3] backends/hostmem: Round up memory size for qemu_madvise() and mbind()

[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 mbind(), since we can't really set policy just to a
fraction of a page. As qemu_madvise() has the same expectation,
round size passed to underlying pagesize.

Signed-off-by: Michal Privoznik <mpriv...@redhat.com>
---
 backends/hostmem.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/backends/hostmem.c b/backends/hostmem.c
index 1a6fd1c714..9b727699f6 100644
--- a/backends/hostmem.c
+++ b/backends/hostmem.c
@@ -179,6 +179,8 @@ static void host_memory_backend_set_merge(Object *obj, bool 
value, Error **errp)
         void *ptr = memory_region_get_ram_ptr(&backend->mr);
         uint64_t sz = memory_region_size(&backend->mr);
 
+        sz = ROUND_UP(sz, qemu_ram_pagesize(backend->mr.ram_block));
+
         if (qemu_madvise(ptr, sz,
                          value ? QEMU_MADV_MERGEABLE : QEMU_MADV_UNMERGEABLE)) 
{
             warn_report("Couldn't change property 'merge' on '%s': %s",
@@ -208,6 +210,8 @@ static void host_memory_backend_set_dump(Object *obj, bool 
value, Error **errp)
         void *ptr = memory_region_get_ram_ptr(&backend->mr);
         uint64_t sz = memory_region_size(&backend->mr);
 
+        sz = ROUND_UP(sz, qemu_ram_pagesize(backend->mr.ram_block));
+
         if (qemu_madvise(ptr, sz,
                          value ? QEMU_MADV_DODUMP : QEMU_MADV_DONTDUMP)) {
             warn_report("Couldn't change property 'dump' on '%s': %s",
@@ -344,6 +348,13 @@ 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
+     * both madvise() and mbind() does not really like setting
+     * advice/policy to just 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)) {
         warn_report("Couldn't set property 'merge' on '%s': %s",
-- 
2.44.1