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

[Thomas Huth <thuth@redhat.com>]

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.

  Thomas