Object debugging tools were sporadically reporting illegal attempts to
free a still active i915 VMA object from when parking a GPU tile believed
to be idle.
[161.359441] ODEBUG: free active (active state 0) object: ffff88811643b958 object type: i915_active hint: __i915_vma_active+0x0/0x50 [i915]
[161.360082] WARNING: CPU: 5 PID: 276 at lib/debugobjects.c:514 debug_print_object+0x80/0xb0
...
[161.360304] CPU: 5 PID: 276 Comm: kworker/5:2 Not tainted 6.5.0-rc1-CI_DRM_13375-g003f860e5577+ #1
[161.360314] Hardware name: Intel Corporation Rocket Lake Client Platform/RocketLake S UDIMM 6L RVP, BIOS RKLSFWI1.R00.3173.A03.2204210138 04/21/2022
[161.360322] Workqueue: i915-unordered __intel_wakeref_put_work [i915]
[161.360592] RIP: 0010:debug_print_object+0x80/0xb0
...
[161.361347] debug_object_free+0xeb/0x110
[161.361362] i915_active_fini+0x14/0x130 [i915]
[161.361866] release_references+0xfe/0x1f0 [i915]
[161.362543] i915_vma_parked+0x1db/0x380 [i915]
[161.363129] __gt_park+0x121/0x230 [i915]
[161.363515] ____intel_wakeref_put_last+0x1f/0x70 [i915]
That has been tracked down to be happening when another thread is
deactivating the VMA inside __active_retire() helper, after the VMA's
active counter has been already decremented to 0, but before deactivation
of the VMA's object is reported to the object debugging tool.
We could prevent from that race by serializing i915_active_fini() with
__active_retire() via ref->tree_lock, but that wouldn't stop the VMA from
being used, e.g. from __i915_vma_retire() called at the end of
__active_retire(), after that VMA has been already freed by a concurrent
i915_vma_destroy() on return from the i915_active_fini(). Then, we should
rather fix the issue at the VMA level, not in i915_active.
Since __i915_vma_parked() is called from __gt_park() on last put of the
GT's wakeref, the issue could be addressed by holding the GT wakeref long
enough for __active_retire() to complete before that wakeref is released
and the GT parked.
A VMA associated with a request doesn't acquire a GT wakeref by itself.
Instead, it depends on a wakeref held directly by the request's active
intel_context for a GT associated with its VM, and indirectly on that
intel_context's engine wakeref if the engine belongs to the same GT as the
VMA's VM. In case of single-tile platforms, at least one of those
wakerefs is usually held long enough for the request's VMA to be
deactivated on time, before it is destroyed on last put of its VM GT
wakeref. However, on multi-tile platforms, a request may use a VMA from a
tile other than the one that hosts the request's engine, then it is
protected only with the intel_context's VM GT wakeref.
There was an attempt to fix this issue on 2-tile Meteor Lake by acquiring
an extra wakeref for a Primary GT from i915_gem_do_execbuffer() -- see
commit f56fe3e91787 ("drm/i915: Fix a VMA UAF for multi-gt platform").
However, it occurred insufficient -- the issue was still reported by CI.
That wakeref was released on exit from i915_gem_do_execbuffer(), then
potentially before completion of the request and deactivation of its
associated VMAs.
OTOH, CI reports indicate that single-tile platforms also suffer
sporadically from the same race.
I believe the issue was introduced by commit d93939730347 ("drm/i915:
Remove the vma refcount") which moved a call to i915_active_fini() from
a dropped i915_vma_release(), called on last put of the removed VMA kref,
to i915_vma_parked() processing path called on last put of a GT wakeref.
However, its visibility to the object debugging tool was suppressed by a
bug in i915_active that was fixed two weeks later with commit e92eb246feb9
("drm/i915/active: Fix missing debug object activation").
Fix the issue by getting a wakeref for the VMA's tile when activating it,
and putting that wakeref only after the VMA is deactivated. However,
exclude global GTT from that processing path, otherwise the GPU never goes
idle. Since __i915_vma_retire() may be called from atomic contexts, use
async variant of wakeref put.
Having that fixed, stop explicitly acquiring the extra GT0 wakeref from
inside i915_gem_do_execbuffer(), and also drop an extra call to
i915_active_wait(), introduced by commit 7a2280e8dcd2 ("drm/i915: Wait for
active retire before i915_active_fini()") as another insufficient fix for
this UAF race.
v3: Identify root cause more precisely, and a commit to blame,
- identify and drop former workarounds,
- update commit message and description.
v2: Get the wakeref before VM mutex to avoid circular locking dependency,
- drop questionable Fixes: tag.
Fixes: d93939730347 ("drm/i915: Remove the vma refcount")
Closes: https://gitlab.freedesktop.org/drm/intel/issues/8875
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Nirmoy Das <nirmoy.das@xxxxxxxxx>
Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.19+
---
.../gpu/drm/i915/gem/i915_gem_execbuffer.c | 21 ++------------
drivers/gpu/drm/i915/i915_vma.c | 28 +++++++++++++------
2 files changed, 21 insertions(+), 28 deletions(-)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 45b9d9e34b8b8..e0c3eaf316e9e 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -2691,7 +2691,6 @@ static int
eb_select_engine(struct i915_execbuffer *eb)
{
struct intel_context *ce, *child;
- struct intel_gt *gt;
unsigned int idx;
int err;
@@ -2715,17 +2714,10 @@ eb_select_engine(struct i915_execbuffer *eb)
}
}
eb->num_batches = ce->parallel.number_children + 1;
- gt = ce->engine->gt;
for_each_child(ce, child)
intel_context_get(child);
- intel_gt_pm_get(gt);
- /*
- * Keep GT0 active on MTL so that i915_vma_parked() doesn't
- * free VMAs while execbuf ioctl is validating VMAs.
- */
- if (gt->info.id)
- intel_gt_pm_get(to_gt(gt->i915));
+ intel_gt_pm_get(ce->engine->gt);
if (!test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
err = intel_context_alloc_state(ce);
@@ -2764,10 +2756,7 @@ eb_select_engine(struct i915_execbuffer *eb)
return err;
err:
- if (gt->info.id)
- intel_gt_pm_put(to_gt(gt->i915));
-
- intel_gt_pm_put(gt);
+ intel_gt_pm_put(ce->engine->gt);
for_each_child(ce, child)
intel_context_put(child);
intel_context_put(ce);
@@ -2780,12 +2769,6 @@ eb_put_engine(struct i915_execbuffer *eb)
struct intel_context *child;
i915_vm_put(eb->context->vm);
- /*
- * This works in conjunction with eb_select_engine() to prevent
- * i915_vma_parked() from interfering while execbuf validates vmas.
- */
- if (eb->gt->info.id)
- intel_gt_pm_put(to_gt(eb->gt->i915));
intel_gt_pm_put(eb->gt);
for_each_child(eb->context, child)
intel_context_put(child);
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index d09aad34ba37f..727123ebfc06e 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -34,6 +34,7 @@
#include "gt/intel_engine.h"
#include "gt/intel_engine_heartbeat.h"
#include "gt/intel_gt.h"
+#include "gt/intel_gt_pm.h"
#include "gt/intel_gt_requests.h"
#include "gt/intel_tlb.h"
@@ -103,12 +104,25 @@ static inline struct i915_vma *active_to_vma(struct i915_active *ref)
static int __i915_vma_active(struct i915_active *ref)
{
- return i915_vma_tryget(active_to_vma(ref)) ? 0 : -ENOENT;
+ struct i915_vma *vma = active_to_vma(ref);
+
+ if (!i915_vma_tryget(vma))
+ return -ENOENT;
+
+ if (!i915_vma_is_ggtt(vma))
+ intel_gt_pm_get(vma->vm->gt);
+
+ return 0;
}
static void __i915_vma_retire(struct i915_active *ref)
{
- i915_vma_put(active_to_vma(ref));
+ struct i915_vma *vma = active_to_vma(ref);
+
+ if (!i915_vma_is_ggtt(vma))
+ intel_gt_pm_put_async(vma->vm->gt);
+
+ i915_vma_put(vma);
}
static struct i915_vma *
@@ -1404,7 +1418,7 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
struct i915_vma_work *work = NULL;
struct dma_fence *moving = NULL;
struct i915_vma_resource *vma_res = NULL;
- intel_wakeref_t wakeref = 0;
+ intel_wakeref_t wakeref;
unsigned int bound;
int err;
@@ -1424,8 +1438,7 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
if (err)
return err;
- if (flags & PIN_GLOBAL)
- wakeref = intel_runtime_pm_get(&vma->vm->i915->runtime_pm);
+ wakeref = intel_runtime_pm_get(&vma->vm->i915->runtime_pm);
if (flags & vma->vm->bind_async_flags) {
/* lock VM */
@@ -1561,8 +1574,7 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww,
if (work)
dma_fence_work_commit_imm(&work->base);
err_rpm:
- if (wakeref)
- intel_runtime_pm_put(&vma->vm->i915->runtime_pm, wakeref);
+ intel_runtime_pm_put(&vma->vm->i915->runtime_pm, wakeref);
if (moving)
dma_fence_put(moving);
@@ -1740,8 +1752,6 @@ static void release_references(struct i915_vma *vma, struct intel_gt *gt,
if (vm_ddestroy)
i915_vm_resv_put(vma->vm);
- /* Wait for async active retire */
- i915_active_wait(&vma->active);
i915_active_fini(&vma->active);
GEM_WARN_ON(vma->resource);
i915_vma_free(vma);
--
2.42.1
