[Intel-gfx] [RFC] drm/i915: Handle E2BIG error in i915_gem_fault

[Michel Thierry]

On 9/9/2015 11:33 AM, Chris Wilson wrote:
> On Wed, Sep 09, 2015 at 11:29:52AM +0100, Michel Thierry wrote:
>> i915_gem_object_bind_to_vm returns -E2BIG when the user tries to bind an
>> object larger than the aperture, but i915_gem_fault does not handle this
>> return code:
>>
>> [501906.530985] gem_mmap_gtt: starting subtest big-bo-tiledX
>> [501906.541992] gem_mmap_gtt (22362): drop_caches: 3
>> [501906.610774] WARNING: CPU: 2 PID: 22362 at
>> drivers/gpu/drm/i915/i915_gem.c:1880 i915_gem_fault+0x24f/0x470 [i915]()
>> [501906.623568] unhandled error in i915_gem_fault: -7
>> [501906.825115] Call Trace:
>> [501906.830322]  [<ffffffff8178ffcc>] dump_stack+0x45/0x57
>> [501906.838589]  [<ffffffff810759aa>] warn_slowpath_common+0x8a/0xc0
>> [501906.847846]  [<ffffffff81075a26>] warn_slowpath_fmt+0x46/0x50
>> [501906.856776]  [<ffffffffc079591f>] i915_gem_fault+0x24f/0x470 [i915]
>> [501906.866276]  [<ffffffff8119e11d>] __do_fault+0x3d/0xa0
>> [501906.874464]  [<ffffffff81068cc0>] ? pte_alloc_one+0x30/0x50
>> [501906.883169]  [<ffffffff811a26a7>] handle_mm_fault+0xe27/0x1810
>> [501906.892202]  [<ffffffff81306e8a>] ? security_mmap_file+0xca/0xe0
>> [501906.900389]  [<ffffffff811fb6ad>] ? do_vfs_ioctl+0x2cd/0x4b0
>> [501906.908143]  [<ffffffff81063ada>] __do_page_fault+0x19a/0x430
>> [501906.916024]  [<ffffffff81063d92>] do_page_fault+0x22/0x30
>> [501906.923532]  [<ffffffff81799248>] page_fault+0x28/0x30
>>
>> RFC about the error code that should be returned by i915_gem_fault.
>
> There are two fixes here, change E2BIG to ENOSPC. The differentiate is
> painful to all consumers (and missing in userspace).

I'll change the return code in gem_object_bind_to_vm instead.

>
> The second is that gem_fault was supposed to be fixed to handle it and
> sigbus is the legimate error for that case (not enomem/sigsegv).

These subtests use objs tiling x/y, so the driver won't use partial views.

Should it be better if i915_gem_mmap_gtt checks for this (obj size 
bigger than apperture and some tiling mode), and return an error at that 
point? Instead of waiting for the sigbus error in gem_fault.

-Michel