On Mon, Sep 23, 2019 at 07:49:01AM -0500, Josh Poimboeuf wrote:
> On Mon, Sep 23, 2019 at 11:20:24AM +0200, Peter Zijlstra wrote:
> > On Wed, Sep 18, 2019 at 09:04:21PM -0700, Randy Dunlap wrote:
> > > On 9/18/19 3:10 PM, Mark Brown wrote:
> > > > Hi all,
> > > >
> > > > Changes since 20190917:
> > > >
> > >
> > > on x86_64:
> > >
> > > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:
> > > i915_gem_execbuffer2_ioctl()+0x2fb: call to gen8_canonical_addr() with
> > > UACCESS enabled
> >
> > I'm thinking that comes from:
> >
> > offset = gen8_canonical_addr(offset & ~UPDATE);
> > if (unlikely(__put_user(offset,
> > &urelocs[r-stack].presumed_offset))) {
> >
> > however, per commit 6ae865615fc4 (and 2a418cf3f5f1) the compiler really
> > should not be sticking gen8_canonical_addr() after __uaccess_begin().
> >
> > /me puzzled...
>
> I think you're looking at the wrong code. It has user_access_begin/end
> around it:
>
> if (!user_access_begin(user_exec_list, count *
> sizeof(*user_exec_list)))
> goto end;
>
> for (i = 0; i < args->buffer_count; i++) {
> if (!(exec2_list[i].offset & UPDATE))
> continue;
>
> exec2_list[i].offset =
> gen8_canonical_addr(exec2_list[i].offset &
> PIN_OFFSET_MASK);
> unsafe_put_user(exec2_list[i].offset,
> &user_exec_list[i].offset,
> end_user);
> }
> end_user:
> user_access_end();
>
Oh, Duh... Yeah, so the alternative to your solution is to do 2 loops.
Not sure which would be better.
