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

[David Hildenbrand <david@redhat.com>]

On 10.08.22 10:11, Thomas Huth wrote:
> On 10/08/2022 09.32, David Hildenbrand wrote:
>> 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);
> 
> Good idea! That way, we could even get rid of the "#ifdef __linux__" macros 
> here, I guess ... I'll give it a try and send a v2 if it works.

At first I wondered if we could have to deal with semi-iniutialized
backendds here, but I think we should simply always already have the
MR/RamBlock here.


-- 
Thanks,

David / dhildenb