Re: [Qemu-devel] [PATCH 1/4] hostmem-memfd: enable seals only if supported

[Marc-André Lureau]

Hi
On Tue, Nov 27, 2018 at 3:56 PM Ilya Maximets <address@hidden> wrote:
>
> On 27.11.2018 14:49, Marc-André Lureau wrote:
> > Hi
> > On Tue, Nov 27, 2018 at 3:11 PM Ilya Maximets <address@hidden> wrote:
> >>
> >> If seals are not supported, memfd_create() will fail.
> >> Furthermore, there is no way to disable it in this case because
> >> '.seal' property is not registered.
> >>
> >> This issue leads to vhost-user-test failures on RHEL 7.2:
> >>
> >>   qemu-system-x86_64: -object memory-backend-memfd,id=mem,size=2M,: \
> >>                       failed to create memfd: Invalid argument
> >>
> >> Signed-off-by: Ilya Maximets <address@hidden>
> >
> >
> > This will change the default behaviour of memfd backend, and may thus
> > me considered a break.
>
> This will change the default behaviour only on systems without sealing
> support. But current implementation is broken there anyway and does not
> work.
>
> >
> > Instead, memfd vhost-user-test should skipped (or tuned with
> > sealed=false if unsupported)
>
> vhost-user-test is just an example here. In fact memfd could not be
> used at all on system without sealing support. And there is no way
> to disable seals.

which system supports memfd without sealing?

>
> >
> >> ---
> >>  backends/hostmem-memfd.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
> >> index b6836b28e5..ee39bdbde6 100644
> >> --- a/backends/hostmem-memfd.c
> >> +++ b/backends/hostmem-memfd.c
> >> @@ -129,8 +129,8 @@ memfd_backend_instance_init(Object *obj)
> >>  {
> >>      HostMemoryBackendMemfd *m = MEMORY_BACKEND_MEMFD(obj);
> >>
> >> -    /* default to sealed file */
> >> -    m->seal = true;
> >> +    /* default to sealed file if supported */
> >> +    m->seal = qemu_memfd_check(MFD_ALLOW_SEALING);
> >>  }
> >>
> >>  static void
> >> --
> >> 2.17.1
> >>
> >
> >
>


-- 
Marc-André Lureau