Re: [PATCH v2 4/4] backends/hostmem: Report error when memory size is unaligned

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Michal,

On 31/5/24 09:29, Michal Privoznik 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 <mprivozn@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);

Can we use size_to_str() instead?

Also display backend name:

"backend '%s' memory size must be multiple of %s"

> +        return;
> +    }
>   
>       if (backend->merge &&
>           qemu_madvise(ptr, sz, QEMU_MADV_MERGEABLE)) {