Re: [PATCH] backends/hostmem: Fix support of memory-backend-memfd in qemu_maxrampagesize()

[David Hildenbrand <david@redhat.com>]

On 10.08.22 08:32, Thomas Huth wrote:
> It is currently not possible yet to use "memory-backend-memfd" on s390x
> with hugepages enabled. This problem is caused by qemu_maxrampagesize()
> not taking memory-backend-memfd objects into account yet, so the code
> in s390_memory_init() fails to enable the huge page support there via
> s390_set_max_pagesize(). Fix it by looking at the memory-backend-memfd
> in the host_memory_backend_pagesize() function, too.
> 
> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=2116496
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  include/sysemu/hostmem.h |  8 +++++++-
>  backends/hostmem-memfd.c |  2 --
>  backends/hostmem.c       | 27 +++++++++++++++++----------
>  3 files changed, 24 insertions(+), 13 deletions(-)
> 
> diff --git a/include/sysemu/hostmem.h b/include/sysemu/hostmem.h
> index 9ff5c16963..d983ae6c01 100644
> --- a/include/sysemu/hostmem.h
> +++ b/include/sysemu/hostmem.h
> @@ -34,10 +34,16 @@ OBJECT_DECLARE_TYPE(HostMemoryBackend, HostMemoryBackendClass,
>  /* hostmem-file.c */
>  /**
>   * @TYPE_MEMORY_BACKEND_FILE:
> - * name of backend that uses mmap on a file descriptor
> + * name of backend that uses mmap on a file
>   */
>  #define TYPE_MEMORY_BACKEND_FILE "memory-backend-file"
>  
> +/* hostmem-memfd.c */
> +/**
> + * @TYPE_MEMORY_BACKEND_MEMFD:
> + * name of backend that uses mmap on a memfd file descriptor
> + */
> +#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
>  
>  /**
>   * HostMemoryBackendClass:
> diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
> index 3fc85c3db8..1ab2085e49 100644
> --- a/backends/hostmem-memfd.c
> +++ b/backends/hostmem-memfd.c
> @@ -18,8 +18,6 @@
>  #include "qapi/error.h"
>  #include "qom/object.h"
>  
> -#define TYPE_MEMORY_BACKEND_MEMFD "memory-backend-memfd"
> -
>  OBJECT_DECLARE_SIMPLE_TYPE(HostMemoryBackendMemfd, MEMORY_BACKEND_MEMFD)
>  
>  
> diff --git a/backends/hostmem.c b/backends/hostmem.c
> index 624bb7ecd3..ebce887105 100644
> --- a/backends/hostmem.c
> +++ b/backends/hostmem.c
> @@ -306,22 +306,29 @@ bool host_memory_backend_is_mapped(HostMemoryBackend *backend)
>      return backend->is_mapped;
>  }
>  
> -#ifdef __linux__
>  size_t host_memory_backend_pagesize(HostMemoryBackend *memdev)
>  {
> +    size_t pagesize = 0;
> +
> +#ifdef __linux__
>      Object *obj = OBJECT(memdev);
> -    char *path = object_property_get_str(obj, "mem-path", NULL);
> -    size_t pagesize = qemu_mempath_getpagesize(path);
>  
> -    g_free(path);
> +    if (object_dynamic_cast(obj, TYPE_MEMORY_BACKEND_FILE)) {
> +        char *path = object_property_get_str(obj, "mem-path", NULL);
> +        pagesize = qemu_mempath_getpagesize(path);
> +        g_free(path);
> +    } else if (object_dynamic_cast(obj, TYPE_MEMORY_BACKEND_MEMFD) &&
> +               object_property_get_bool(obj, "hugetlb", &error_abort)) {
> +        pagesize = object_property_get_int(obj, "hugetlbsize", &error_abort);
> +    }
> +#endif

Why can't we simply rely on

qemu_ram_pagesize(memdev->mr.ram_block);

?

-- 
Thanks,

David / dhildenb