[Intel-gfx] [PATCH] drm/i915: Convert WARNs during userptr revoke to SIGBUS

[Chris Wilson]

If the client revokes the virtual address it asked to be mapped into GPU
space via userptr (by using anything along the lines of mmap, mprotect,
madvise, munmap, ftruncate etc) the mmu notifier sends a range
invalidate command to userptr. Upon receiving the invalidation signal
for the revoked range, we try to release the struct pages we pinned into
the GTT. However, this can fail if any of the GPU's VMA are pinned for
use by the hardware (i.e. despite the user's intention we cannot
relinquish the client's address range and keep uptodate with whatever is
placed in there). Currently we emit a few WARN so that we would notice
if this every occurred in the wild; it has. Sadly this means we need to
replace those WARNs with the proper SIGBUS to the offending clients
instead.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Michał Winiarski <michal.winiarski at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_userptr.c | 41 +++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index f75d90118888..efb404b9fe69 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -81,11 +81,44 @@ static void __cancel_userptr__worker(struct work_struct *work)
 		was_interruptible = dev_priv->mm.interruptible;
 		dev_priv->mm.interruptible = false;
 
-		list_for_each_entry_safe(vma, tmp, &obj->vma_list, obj_link) {
-			int ret = i915_vma_unbind(vma);
-			WARN_ON(ret && ret != -EIO);
+		list_for_each_entry_safe(vma, tmp, &obj->vma_list, obj_link)
+			i915_vma_unbind(vma);
+		if (i915_gem_object_put_pages(obj)) {
+			struct task_struct *p;
+
+			DRM_ERROR("Unable to revoke ownership by userptr of"
+				  " invalidated address range, sending SIGBUS"
+				  " to attached clients.\n");
+
+			rcu_read_lock();
+			for_each_process(p) {
+				siginfo_t info;
+
+				/* This doesn't capture everyone who has
+				 * the pages pinned behind a VMA as we
+				 * do not have that tracking information
+				 * available, it does however kill the
+				 * original process (and siblings) who
+				 * created the userptr and presumably tried
+				 * to reuse the address space despite having
+				 * pinned it (possibly indirectly) to the hw.
+				 * Arguably, we don't even want to kill the
+				 * other processes as they are not at fault,
+				 * likely to be a display server, and hopefully
+				 * will release the pages in due course once
+				 * the client is dead.
+				 */
+				if (p->mm != obj->userptr.mm->mm)
+					continue;
+
+				info.si_signo = SIGBUS;
+				info.si_errno = 0;
+				info.si_code = BUS_ADRERR;
+				info.si_addr = (void __user *)obj->userptr.ptr;
+				force_sig_info(SIGBUS, &info, p);
+			}
+			rcu_read_unlock();
 		}
-		WARN_ON(i915_gem_object_put_pages(obj));
 
 		dev_priv->mm.interruptible = was_interruptible;
 	}
-- 
2.5.3