On 08/03/2017 10:01, Chris Wilson wrote:
On Wed, Mar 08, 2017 at 08:25:12AM +0000, Tvrtko Ursulin wrote:
On 07/03/2017 20:58, Chris Wilson wrote:
If we allow the user to convert a GTT mmap address into a userptr, we
may end up in recursion hell, where currently we hit a mutex deadlock
but other possibilities include use-after-free during the
unbind/cancel_userptr.
[ 143.203989] gem_userptr_bli D 0 902 898 0x00000000
[ 143.204054] Call Trace:
[ 143.204137] __schedule+0x511/0x1180
[ 143.204195] ? pci_mmcfg_check_reserved+0xc0/0xc0
[ 143.204274] schedule+0x57/0xe0
[ 143.204327] schedule_timeout+0x383/0x670
[ 143.204374] ? trace_hardirqs_on_caller+0x187/0x280
[ 143.204457] ? trace_hardirqs_on_thunk+0x1a/0x1c
[ 143.204507] ? usleep_range+0x110/0x110
[ 143.204657] ? irq_exit+0x89/0x100
[ 143.204710] ? retint_kernel+0x2d/0x2d
[ 143.204794] ? trace_hardirqs_on_caller+0x187/0x280
[ 143.204857] ? _raw_spin_unlock_irq+0x33/0x60
[ 143.204944] wait_for_common+0x1f0/0x2f0
[ 143.205006] ? out_of_line_wait_on_atomic_t+0x170/0x170
[ 143.205103] ? wake_up_q+0xa0/0xa0
[ 143.205159] ? flush_workqueue_prep_pwqs+0x15a/0x2c0
[ 143.205237] wait_for_completion+0x1d/0x20
[ 143.205292] flush_workqueue+0x2e9/0xbb0
[ 143.205339] ? flush_workqueue+0x163/0xbb0
[ 143.205418] ? __schedule+0x533/0x1180
[ 143.205498] ? check_flush_dependency+0x1a0/0x1a0
[ 143.205681] i915_gem_userptr_mn_invalidate_range_start+0x1c7/0x270 [i915]
[ 143.205865] ? i915_gem_userptr_dmabuf_export+0x40/0x40 [i915]
[ 143.205955] __mmu_notifier_invalidate_range_start+0xc6/0x120
[ 143.206044] ? __mmu_notifier_invalidate_range_start+0x51/0x120
[ 143.206123] zap_page_range_single+0x1c7/0x1f0
[ 143.206171] ? unmap_single_vma+0x160/0x160
[ 143.206260] ? unmap_mapping_range+0xa9/0x1b0
[ 143.206308] ? vma_interval_tree_subtree_search+0x75/0xd0
[ 143.206397] unmap_mapping_range+0x18f/0x1b0
[ 143.206444] ? zap_vma_ptes+0x70/0x70
[ 143.206524] ? __pm_runtime_resume+0x67/0xa0
[ 143.206723] i915_gem_release_mmap+0x1ba/0x1c0 [i915]
[ 143.206846] i915_vma_unbind+0x5c2/0x690 [i915]
[ 143.206925] ? __lock_is_held+0x52/0x100
[ 143.207076] i915_gem_object_set_tiling+0x1db/0x650 [i915]
[ 143.207236] i915_gem_set_tiling_ioctl+0x1d3/0x3b0 [i915]
[ 143.207377] ? i915_gem_set_tiling_ioctl+0x5/0x3b0 [i915]
[ 143.207457] drm_ioctl+0x36c/0x670
[ 143.207535] ? debug_lockdep_rcu_enabled.part.0+0x1a/0x30
[ 143.207730] ? i915_gem_object_set_tiling+0x650/0x650 [i915]
[ 143.207793] ? drm_getunique+0x120/0x120
[ 143.207875] ? __handle_mm_fault+0x996/0x14a0
[ 143.207939] ? vm_insert_page+0x340/0x340
[ 143.208028] ? up_write+0x28/0x50
[ 143.208086] ? vm_mmap_pgoff+0x160/0x190
[ 143.208163] do_vfs_ioctl+0x12c/0xa60
[ 143.208218] ? debug_lockdep_rcu_enabled+0x35/0x40
[ 143.208267] ? ioctl_preallocate+0x150/0x150
[ 143.208353] ? __do_page_fault+0x36a/0x6e0
[ 143.208400] ? mark_held_locks+0x23/0xc0
[ 143.208479] ? up_read+0x1f/0x40
[ 143.208526] ? entry_SYSCALL_64_fastpath+0x5/0xc6
[ 143.208669] ? __fget_light+0xa7/0xc0
[ 143.208747] SyS_ioctl+0x41/0x70
To prevent the possibility of a deadlock, we defer scheduling the worker
until after we have proven that given the current mm, the userptr range
does not overlap a GGTT mmaping. If another thread tries to remap the
GGTT over the userptr before the worker is scheduled, it will be stopped
by its invalidate-range flushing the current work, before the deadlock
can occur.
v2: Improve discussion of how we end up in the deadlock.
Reported-by: Michał Winiarski <michal.winiarski@xxxxxxxxx>
Testcase: igt/gem_userptr_blits/map-fixed-invalidate-gup
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem_userptr.c | 76 ++++++++++++++++++++++-----------
1 file changed, 52 insertions(+), 24 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index dc9bf5282071..7addbf08bcb9 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -488,6 +488,36 @@ __i915_gem_userptr_set_active(struct drm_i915_gem_object *obj,
return ret;
}
+static bool overlaps_ggtt(struct drm_i915_gem_object *obj, struct mm_struct *mm)
+{
+ const struct vm_operations_struct *gem_vm_ops =
+ obj->base.dev->driver->gem_vm_ops;
+ unsigned long addr = obj->userptr.ptr;
+ const unsigned long end = addr + obj->base.size;
+ struct vm_area_struct *vma;
+
+ /* Check for a contiguous set of vma covering the userptr, if any
+ * are absent, they will EFAULT. More importantly if any point back
+ * to a drm_i915_gem_object GTT mmaping, we may trigger a deadlock
+ * between the deferred gup of this userptr and the object being
+ * unbound calling invalidate_range -> cancel_userptr.
+ */
+ for (vma = find_vma(mm, addr); vma; vma = vma->vm_next) {
+ if (vma->vm_start > addr) /* gap */
+ break;
If I understand this correctly it is checking for more than ggtt, so
would be tempted to either remove those parts of the checks or
remove the helper to something like invalid_backing_store.
Also, again if I understand it correctly, if the backing store was
made out of two VMAs then wouldn't this return a false positive?
No. The vmas have to be contiguous or else the range covers an absent
page (which will EFAULT).
I assume you imply there cannot be two adjacent VMAs, that the core
would merge them? But I am thinking there could be two non-mergeable
ones if the backing store was different. Not 100% sure, this is just my
intuition talking. But it would still be a valid userptr object, one
half backed with anon pages, another say file backed.
Regards,
Tvrtko
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