[Qemu-devel] [PATCH] exec.c: Ensure right alignment also for file backed ram

[Dominik Dingel <dingel@linux.vnet.ibm.com>]

While in the anonymous ram case we already take care of the right alignment
such an alignment gurantee does not exist for file backed ram allocation.

Instead, pagesize is used for alignment. On s390 this is not enough for gmap,
as we need to satisfy an alignment up to segments.

Reported-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>

---

I thought about moving this alignment into qemu_ram_mmap but the result
was a lot of code churn, the other possibility was to create an additional
define ending up with two defines with the same semantics.

---
 exec.c               | 16 ++++++++--------
 include/qemu/osdep.h | 12 ++++++++++++
 util/oslib-posix.c   | 12 ------------
 3 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/exec.c b/exec.c
index f398d21..2c4583f 100644
--- a/exec.c
+++ b/exec.c
@@ -1239,7 +1239,7 @@ static void *file_ram_alloc(RAMBlock *block,
     char *c;
     void *area;
     int fd;
-    int64_t page_size;
+    int64_t alignment;
 
     if (kvm_enabled() && !kvm_has_sync_mmu()) {
         error_setg(errp,
@@ -1294,17 +1294,17 @@ static void *file_ram_alloc(RAMBlock *block,
          */
     }
 
-    page_size = qemu_fd_getpagesize(fd);
-    block->mr->align = page_size;
+    alignment = MAX(qemu_fd_getpagesize(fd), QEMU_VMALLOC_ALIGN);
+    block->mr->align = alignment;
 
-    if (memory < page_size) {
+    if (memory < alignment) {
         error_setg(errp, "memory size 0x" RAM_ADDR_FMT " must be equal to "
-                   "or larger than page size 0x%" PRIx64,
-                   memory, page_size);
+                   "or larger than needed alignment 0x%" PRIx64,
+                   memory, alignment);
         goto error;
     }
 
-    memory = ROUND_UP(memory, page_size);
+    memory = ROUND_UP(memory, alignment);
 
     /*
      * ftruncate is not supported by hugetlbfs in older
@@ -1316,7 +1316,7 @@ static void *file_ram_alloc(RAMBlock *block,
         perror("ftruncate");
     }
 
-    area = qemu_ram_mmap(fd, memory, page_size, block->flags & RAM_SHARED);
+    area = qemu_ram_mmap(fd, memory, alignment, block->flags & RAM_SHARED);
     if (area == MAP_FAILED) {
         error_setg_errno(errp, errno,
                          "unable to map backing store for guest RAM");
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 5bb374c..3d81672 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -231,6 +231,18 @@ void qemu_anon_ram_free(void *ptr, size_t size);
 
 #endif
 
+#if defined(__linux__) && (defined(__x86_64__) || defined(__arm__))
+   /* Use 2 MiB alignment so transparent hugepages can be used by KVM.
+      Valgrind does not support alignments larger than 1 MiB,
+      therefore we need special code which handles running on Valgrind. */
+#  define QEMU_VMALLOC_ALIGN (512 * 4096)
+#elif defined(__linux__) && defined(__s390x__)
+   /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
+#  define QEMU_VMALLOC_ALIGN (256 * 4096)
+#else
+#  define QEMU_VMALLOC_ALIGN getpagesize()
+#endif
+
 int qemu_madvise(void *addr, size_t len, int advice);
 
 int qemu_open(const char *name, int flags, ...);
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 05c44ed..52c621f 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -26,18 +26,6 @@
  * THE SOFTWARE.
  */
 
-#if defined(__linux__) && (defined(__x86_64__) || defined(__arm__))
-   /* Use 2 MiB alignment so transparent hugepages can be used by KVM.
-      Valgrind does not support alignments larger than 1 MiB,
-      therefore we need special code which handles running on Valgrind. */
-#  define QEMU_VMALLOC_ALIGN (512 * 4096)
-#elif defined(__linux__) && defined(__s390x__)
-   /* Use 1 MiB (segment size) alignment so gmap can be used by KVM. */
-#  define QEMU_VMALLOC_ALIGN (256 * 4096)
-#else
-#  define QEMU_VMALLOC_ALIGN getpagesize()
-#endif
-
 #include "qemu/osdep.h"
 #include <termios.h>
 #include <termios.h>
-- 
2.6.5