[Qemu-devel] [RFC PATCH] file ram alloc: fail if cannot preallocate

[Alexey Kardashevskiy <aik@ozlabs.ru>]

At the moment if the user asked for huge pages and there is no more huge
pages, QEMU prints warning and falls back to the anonymous memory
allocator which is quite easy not to notice. QEMU also does so even
if the user specified -mem-prealloc and it seems wrong as the user
specifically requested huge pages for the entire RAM but QEMU failed to do
so and continued. On PPC64 this will produce a fragile guest as QEMU
tells the guest via device-tree that it can use huge pages when it
actually cannot.

This adds message+exit if RAM cannot be preallocated from huge pages.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 exec.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/exec.c b/exec.c
index 9ad0a4b..deb8279 100644
--- a/exec.c
+++ b/exec.c
@@ -1041,6 +1041,10 @@ static void *file_ram_alloc(RAMBlock *block,
 
     area = mmap(0, memory, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
     if (area == MAP_FAILED) {
+        if (mem_prealloc) {
+            perror("file_ram_alloc: failed to preallocate RAM");
+            exit(1);
+        }
         perror("file_ram_alloc: can't mmap RAM pages");
         close(fd);
         return (NULL);
-- 
1.8.4.rc4