See the following for many more details.
commit acc240d41ea1ab9c488a79219fb313b5b46265ae
Author: Daniel Vetter <daniel.vetter@xxxxxxxx>
Date: Thu Dec 5 15:42:34 2013 +0100
drm/i915: Fix use-after-free in do_switch
In this case, the issue is only for full PPGTT:
do_switch
context_unref
ppgtt_release
i915_gpu_idle
switch_to_default
from changes to default context
This could be backported to the pre do_switch cleanup I did in this
series. However, it's much cleaner and more obvious as a patch on top,
so I'd really like to do this as a post cleanup patch.
v2: There was a bug in the original patch where the ring->last_context
was set too early. I am not sure how this wasn't being hit when I sent
this previously. Perhaps I tested the wrong patch previously.
Signed-off-by: Ben Widawsky <ben@xxxxxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem_context.c | 24 +++++++++++++++++-------
1 file changed, 17 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c9aa3e6..0ce8fc9 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -609,14 +609,18 @@ mi_set_context(struct intel_engine_cs *ring,
return ret;
}
-static void do_switch_fini_common(struct intel_engine_cs *ring,
- struct intel_context *from,
- struct intel_context *to)
+static struct intel_context *do_switch_fini_common(struct intel_engine_cs *ring,
+ struct intel_context *from,
+ struct intel_context *to)
{
+ struct intel_context *ret;
if (likely(from))
i915_gem_context_unreference(from);
i915_gem_context_reference(to);
+ ret = ring->last_context;
ring->last_context = to;
+
+ return ret;
}
static int do_switch_xcs(struct intel_engine_cs *ring,
@@ -762,14 +766,20 @@ static int do_switch_rcs(struct intel_engine_cs *ring,
*/
from->legacy_hw_ctx.rcs_state->dirty = 1;
BUG_ON(from->legacy_hw_ctx.rcs_state->ring != ring);
-
- /* obj is kept alive until the next request by its active ref */
- i915_gem_object_ggtt_unpin(from->legacy_hw_ctx.rcs_state);
}
uninitialized = !to->legacy_hw_ctx.initialized && from == NULL;
to->legacy_hw_ctx.initialized = true;
- do_switch_fini_common(ring, from, to);
+ /* From may have disappeared again after the context unref */
+ from = do_switch_fini_common(ring, from, to);
+ if (from != NULL) {
+ /* obj is kept alive until the next request by its active ref.
+ * XXX: The context needs to be unpinned last, or else we risk
+ * hitting evict/idle on the ppgtt free, which will call back
+ * into this, and we'll get a double unpin on this context
+ */
+ i915_gem_object_ggtt_unpin(from->legacy_hw_ctx.rcs_state);
+ }
if (uninitialized) {
ret = i915_gem_render_state_init(ring);
--
2.0.4
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