This patch has been successfully tested by QE. After allocating some
hugepages in the host, try to boot up a VM with the memory backed by a
file and the size unaligned, check now the message displayed by QEMU:
qemu-system-x86_64: backend memory size must be multiple of 0x200000
Tested-by: Mario Casquero <mcasq...@redhat.com>
On Fri, May 31, 2024 at 9:29 AM Michal Privoznik <mpriv...@redhat.com> wrote:
>
> If memory-backend-{file,ram} has a size that's not aligned to
> underlying page size it is not only wasteful, but also may lead
> to hard to debug behaviour. For instance, in case
> memory-backend-file and hugepages, madvise() and mbind() fail.
> Rightfully so, page is the smallest unit they can work with. And
> even though an error is reported, the root cause it not very
> clear:
>
> qemu-system-x86_64: Couldn't set property 'dump' on 'memory-backend-file':
> Invalid argument
>
> After this commit:
>
> qemu-system-x86_64: backend memory size must be multiple of 0x200000
>
> Signed-off-by: Michal Privoznik <mpriv...@redhat.com>
> ---
> backends/hostmem.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/backends/hostmem.c b/backends/hostmem.c
> index 012a8c190f..5f9c9ea8f5 100644
> --- a/backends/hostmem.c
> +++ b/backends/hostmem.c
> @@ -337,6 +337,7 @@ host_memory_backend_memory_complete(UserCreatable *uc,
> Error **errp)
> HostMemoryBackendClass *bc = MEMORY_BACKEND_GET_CLASS(uc);
> void *ptr;
> uint64_t sz;
> + size_t pagesize;
> bool async = !phase_check(PHASE_LATE_BACKENDS_CREATED);
>
> if (!bc->alloc) {
> @@ -348,6 +349,13 @@ host_memory_backend_memory_complete(UserCreatable *uc,
> Error **errp)
>
> ptr = memory_region_get_ram_ptr(&backend->mr);
> sz = memory_region_size(&backend->mr);
> + pagesize = qemu_ram_pagesize(backend->mr.ram_block);
> +
> + if (!QEMU_IS_ALIGNED(sz, pagesize)) {
> + error_setg(errp, "backend memory size must be multiple of 0x%"
> + PRIx64, pagesize);
> + return;
> + }
>
> if (backend->merge &&
> qemu_madvise(ptr, sz, QEMU_MADV_MERGEABLE)) {
> --
> 2.44.1
>
>
