Am 21.08.2019 20:28 schrieb "Thomas Hellström (VMware)" <thomas...@shipmail.org>: On 8/21/19 8:11 PM, Daniel Vetter wrote: > On Wed, Aug 21, 2019 at 7:06 PM Thomas Hellström (VMware) > <thomas...@shipmail.org> wrote: >> On 8/21/19 6:34 PM, Daniel Vetter wrote: >>> On Wed, Aug 21, 2019 at 05:54:27PM +0200, Thomas Hellström (VMware) wrote: >>>> On 8/20/19 4:53 PM, Daniel Vetter wrote: >>>>> Full audit of everyone: >>>>> >>>>> - i915, radeon, amdgpu should be clean per their maintainers. >>>>> >>>>> - vram helpers should be fine, they don't do command submission, so >>>>> really no business holding struct_mutex while doing copy_*_user. But >>>>> I haven't checked them all. >>>>> >>>>> - panfrost seems to dma_resv_lock only in panfrost_job_push, which >>>>> looks clean. >>>>> >>>>> - v3d holds dma_resv locks in the tail of its v3d_submit_cl_ioctl(), >>>>> copying from/to userspace happens all in v3d_lookup_bos which is >>>>> outside of the critical section. >>>>> >>>>> - vmwgfx has a bunch of ioctls that do their own copy_*_user: >>>>> - vmw_execbuf_process: First this does some copies in >>>>> vmw_execbuf_cmdbuf() and also in the vmw_execbuf_process() itself. >>>>> Then comes the usual ttm reserve/validate sequence, then actual >>>>> submission/fencing, then unreserving, and finally some more >>>>> copy_to_user in vmw_execbuf_copy_fence_user. Glossing over tons of >>>>> details, but looks all safe. >>>>> - vmw_fence_event_ioctl: No ttm_reserve/dma_resv_lock anywhere to be >>>>> seen, seems to only create a fence and copy it out. >>>>> - a pile of smaller ioctl in vmwgfx_ioctl.c, no reservations to be >>>>> found there. >>>>> Summary: vmwgfx seems to be fine too. >>>>> >>>>> - virtio: There's virtio_gpu_execbuffer_ioctl, which does all the >>>>> copying from userspace before even looking up objects through their >>>>> handles, so safe. Plus the getparam/getcaps ioctl, also both safe. >>>>> >>>>> - qxl only has qxl_execbuffer_ioctl, which calls into >>>>> qxl_process_single_command. There's a lovely comment before the >>>>> __copy_from_user_inatomic that the slowpath should be copied from >>>>> i915, but I guess that never happened. Try not to be unlucky and get >>>>> your CS data evicted between when it's written and the kernel tries >>>>> to read it. The only other copy_from_user is for relocs, but those >>>>> are done before qxl_release_reserve_list(), which seems to be the >>>>> only thing reserving buffers (in the ttm/dma_resv sense) in that >>>>> code. So looks safe. >>>>> >>>>> - A debugfs file in nouveau_debugfs_pstate_set() and the usif ioctl in >>>>> usif_ioctl() look safe. nouveau_gem_ioctl_pushbuf() otoh breaks this >>>>> everywhere and needs to be fixed up. >>>>> >>>>> Cc: Alex Deucher <alexander.deuc...@amd.com> >>>>> Cc: Christian König <christian.koe...@amd.com> >>>>> Cc: Chris Wilson <ch...@chris-wilson.co.uk> >>>>> Cc: Thomas Zimmermann <tzimmerm...@suse.de> >>>>> Cc: Rob Herring <r...@kernel.org> >>>>> Cc: Tomeu Vizoso <tomeu.viz...@collabora.com> >>>>> Cc: Eric Anholt <e...@anholt.net> >>>>> Cc: Dave Airlie <airl...@redhat.com> >>>>> Cc: Gerd Hoffmann <kra...@redhat.com> >>>>> Cc: Ben Skeggs <bske...@redhat.com> >>>>> Cc: "VMware Graphics" <linux-graphics-maintai...@vmware.com> >>>>> Cc: Thomas Hellstrom <thellst...@vmware.com> >>>>> Signed-off-by: Daniel Vetter <daniel.vet...@intel.com> >>>>> --- >>>>> drivers/dma-buf/dma-resv.c | 12 ++++++++++++ >>>>> 1 file changed, 12 insertions(+) >>>>> >>>>> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c >>>>> index 42a8f3f11681..3edca10d3faf 100644 >>>>> --- a/drivers/dma-buf/dma-resv.c >>>>> +++ b/drivers/dma-buf/dma-resv.c >>>>> @@ -34,6 +34,7 @@ >>>>> #include <linux/dma-resv.h> >>>>> #include <linux/export.h> >>>>> +#include <linux/sched/mm.h> >>>>> /** >>>>> * DOC: Reservation Object Overview >>>>> @@ -107,6 +108,17 @@ void dma_resv_init(struct dma_resv *obj) >>>>> &reservation_seqcount_class); >>>>> RCU_INIT_POINTER(obj->fence, NULL); >>>>> RCU_INIT_POINTER(obj->fence_excl, NULL); >>>>> + >>>>> + if (IS_ENABLED(CONFIG_LOCKDEP)) { >>>>> + if (current->mm) >>>>> + down_read(¤t->mm->mmap_sem); >>>>> + ww_mutex_lock(&obj->lock, NULL); >>>>> + fs_reclaim_acquire(GFP_KERNEL); >>>>> + fs_reclaim_release(GFP_KERNEL); >>>>> + ww_mutex_unlock(&obj->lock); >>>>> + if (current->mm) >>>>> + up_read(¤t->mm->mmap_sem); >>>>> + } >>>>> } >>>>> EXPORT_SYMBOL(dma_resv_init); >>>> I assume if this would have been easily done and maintainable using only >>>> lockdep annotation instead of actually acquiring the locks, that would have >>>> been done? >>> There's might_lock(), plus a pile of macros, but they don't map obviuosly, >>> so pretty good chances I accidentally end up with the wrong type of >>> annotation. Easier to just take the locks quickly, and stuff that all into >>> a lockdep-only section to avoid overhead. >>> >>>> Otherwise LGTM. >>>> >>>> Reviewed-by: Thomas Hellström <thellst...@vmware.com> >>>> >>>> Will test this and let you know if it trips on vmwgfx, but it really >>>> shouldn't. >>> Thanks, Daniel >> One thing that strikes me is that this puts restrictions on where you >> can actually initialize a dma_resv, even if locking orders are otherwise >> obeyed. But that might not be a big problem. > Hm yeah ... the trouble is a need a non-kthread thread so that I have > a current->mm. Otherwise I'd have put it into some init section with a > temp dma_buf. And I kinda don't want to create a fake ->mm just for > lockdep priming. I don't expect this to be a real problem in practice, > since before you've called dma_resv_init the reservation lock doesn't > exist, so you can't hold it. And you've probably just allocated it, so > fs_reclaim is going to be fine. And if you allocate dma_resv objects > from your fault handlers I have questions anyway :-)
Coming to think of it, I think vmwgfx sometimes create bos with other bo's reservation lock held. I guess that would trip both the mmap_sem check the ww_mutex check? Dito inside TTM for ghost objects. We even used to have an dma_resv_init() in an atomic section, but that should be gone by now. Anyway, probably have to take my review back since this will certainly go up in flames. Need a better place for this, Christian. /Thomas /Thomas > > So I think this should be safe. > -Daniel
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