[PATCH] Revert "drm/i915: Remove extra multi-gt pm-references"

Tue May 7 07:30:15 UTC 2024

Hi Janusz,

Just realized we need Fixes tag for this.

Fixes: 1f33dc0c1189 ("drm/i915: Remove extra multi-gt pm-references")

Regards,

Nirmoy

On 5/6/2024 8:02 PM, Janusz Krzysztofik wrote:
> This reverts commit 1f33dc0c1189efb9ae19c6fc22b64dd3e26261fb.
>
> There was a patch supposed to fix an issue of illegal attempts to free a
> still active i915 VMA object when parking a GT believed to be idle,
> reported by CI on 2-GT Meteor Lake.  As a solution, an extra wakeref for
> a Primary GT was acquired from i915_gem_do_execbuffer() -- see commit
> f56fe3e91787 ("drm/i915: Fix a VMA UAF for multi-gt platform").
>
> However, that fix 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.  Moreover, CI reports indicated that single-GT platforms
> also suffered sporadically from the same race.
>
> Since that issue was fixed by another commit f3c71b2ded5c ("drm/i915/vma:
> Fix UAF on destroy against retire race"), the changes introduced by that
> insufficient fix were dropped as no longer useful.  However, that series
> resulted in another VMA UAF scenario now being triggered in CI.
>
> <4> [260.290809] ------------[ cut here ]------------
> <4> [260.290988] list_del corruption. prev->next should be ffff888118c5d990, but was ffff888118c5a510. (prev=ffff888118c5a510)
> <4> [260.291004] WARNING: CPU: 2 PID: 1143 at lib/list_debug.c:62 __list_del_entry_valid_or_report+0xb7/0xe0
> ..
> <4> [260.291055] CPU: 2 PID: 1143 Comm: kms_plane Not tainted 6.9.0-rc2-CI_DRM_14524-ga25d180c6853+ #1
> <4> [260.291058] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
> <4> [260.291060] RIP: 0010:__list_del_entry_valid_or_report+0xb7/0xe0
> ...
> <4> [260.291087] Call Trace:
> <4> [260.291089]  <TASK>
> <4> [260.291124]  i915_vma_reopen+0x43/0x80 [i915]
> <4> [260.291298]  eb_lookup_vmas+0x9cb/0xcc0 [i915]
> <4> [260.291579]  i915_gem_do_execbuffer+0xc9a/0x26d0 [i915]
> <4> [260.291883]  i915_gem_execbuffer2_ioctl+0x123/0x2a0 [i915]
> ...
> <4> [260.292301]  </TASK>
> ...
> <4> [260.292506] ---[ end trace 0000000000000000 ]---
> <4> [260.292782] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6ca3: 0000 [#1] PREEMPT SMP NOPTI
> <4> [260.303575] CPU: 2 PID: 1143 Comm: kms_plane Tainted: G        W          6.9.0-rc2-CI_DRM_14524-ga25d180c6853+ #1
> <4> [260.313851] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024
> <4> [260.326359] RIP: 0010:eb_validate_vmas+0x114/0xd80 [i915]
> ...
> <4> [260.428756] Call Trace:
> <4> [260.431192]  <TASK>
> <4> [639.283393]  i915_gem_do_execbuffer+0xd05/0x26d0 [i915]
> <4> [639.305245]  i915_gem_execbuffer2_ioctl+0x123/0x2a0 [i915]
> ...
> <4> [639.411134]  </TASK>
> ...
> <4> [639.449979] ---[ end trace 0000000000000000 ]---
>
> We defer actually closing, unbinding and destroying a VMA until next idle
> point, or until the object is freed in the meantime.  By postponing the
> unbind, we allow for the VMA to be reopened by the client, avoiding the
> work required to rebind the VMA.
>
> Starting from commit b0647a5e79b1 ("drm/i915: Avoid live-lock with
> i915_vma_parked()"), we assume that as long as a GT is held idle, no VMA
> would be reopened while we destroy them.  That assumption is no longer
> true in multi-GT configurations, where a VMA we reopen may be handled by a
> GT different from the one that we already keep active via its engine while
> we set up an execbuf request.
>
> Restoring the extra GT0 PM wakeref removed from i915_gem_do_execbuffer()
> processing path seems to fix this issue.
>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/10608
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Nirmoy Das <nirmoy.das at linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 42619fc05de48..090724fa766c9 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -255,6 +255,7 @@ struct i915_execbuffer {
>   	struct intel_context *context; /* logical state for the request */
>   	struct i915_gem_context *gem_context; /** caller's context */
>   	intel_wakeref_t wakeref;
> +	intel_wakeref_t wakeref_gt0;
>   
>   	/** our requests to build */
>   	struct i915_request *requests[MAX_ENGINE_INSTANCE + 1];
> @@ -2685,6 +2686,7 @@ static int
>   eb_select_engine(struct i915_execbuffer *eb)
>   {
>   	struct intel_context *ce, *child;
> +	struct intel_gt *gt;
>   	unsigned int idx;
>   	int err;
>   
> @@ -2708,10 +2710,17 @@ 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);
>   	eb->wakeref = intel_gt_pm_get(ce->engine->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)
> +		eb->wakeref_gt0 = intel_gt_pm_get(to_gt(gt->i915));
>   
>   	if (!test_bit(CONTEXT_ALLOC_BIT, &ce->flags)) {
>   		err = intel_context_alloc_state(ce);
> @@ -2750,6 +2759,9 @@ eb_select_engine(struct i915_execbuffer *eb)
>   	return err;
>   
>   err:
> +	if (gt->info.id)
> +		intel_gt_pm_put(to_gt(gt->i915), eb->wakeref_gt0);
> +
>   	intel_gt_pm_put(ce->engine->gt, eb->wakeref);
>   	for_each_child(ce, child)
>   		intel_context_put(child);
> @@ -2763,6 +2775,12 @@ 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), eb->wakeref_gt0);
>   	intel_gt_pm_put(eb->context->engine->gt, eb->wakeref);
>   	for_each_child(eb->context, child)
>   		intel_context_put(child);