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

[Stefan Hajnoczi <stefanha@gmail.com>]

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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

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