Re: [Qemu-devel] [PATCH] memory: fetch pmem size in get_file_size()

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/09/19 12:25, Stefan Hajnoczi wrote:
> On Fri, Aug 30, 2019 at 03:44:45PM -0300, Eduardo Habkost wrote:
>> On Fri, Aug 30, 2019 at 10:30:56AM +0100, Stefan Hajnoczi wrote:
>>> Neither stat(2) nor lseek(2) report the size of Linux devdax pmem
>>> character device nodes.  Commit 314aec4a6e06844937f1677f6cba21981005f389
>>> ("hostmem-file: reject invalid pmem file sizes") added code to
>>> hostmem-file.c to fetch the size from sysfs and compare against the
>>> user-provided size=NUM parameter:
>>>
>>>   if (backend->size > size) {
>>>       error_setg(errp, "size property %" PRIu64 " is larger than "
>>>                  "pmem file \"%s\" size %" PRIu64, backend->size,
>>>                  fb->mem_path, size);
>>>       return;
>>>   }
>>>
>>> It turns out that exec.c:qemu_ram_alloc_from_fd() already has an
>>> equivalent size check but it skips devdax pmem character devices because
>>> lseek(2) returns 0:
>>>
>>>   if (file_size > 0 && file_size < size) {
>>>       error_setg(errp, "backing store %s size 0x%" PRIx64
>>>                  " does not match 'size' option 0x" RAM_ADDR_FMT,
>>>                  mem_path, file_size, size);
>>>       return NULL;
>>>   }
>>>
>>> This patch moves the devdax pmem file size code into get_file_size() so
>>> that we check the memory size in a single place:
>>> qemu_ram_alloc_from_fd().  This simplifies the code and makes it more
>>> general.
>>>
>>> This also fixes the problem that hostmem-file only checks the devdax
>>> pmem file size when the pmem=on parameter is given.  An unchecked
>>> size=NUM parameter can lead to SIGBUS in QEMU so we must always fetch
>>> the file size for Linux devdax pmem character device nodes.
>>>
>>> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>>
>> Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
>>
>> Paolo, do you want to queue this, or should it go through my
>> memory backend queue?
> 
> Ping for Paolo

I had actually queued it already, thanks.

Paolo