Re: [PATCH v2 3/5] drm/xe/vf: Wait for default LRCs fixups before using

["Lis, Tomasz" <tomasz.lis@intel.com>]

On 2/19/2026 9:40 PM, Matthew Brost wrote:
> On Thu, Feb 19, 2026 at 12:16:49PM -0800, Matthew Brost wrote:
>> On Thu, Feb 19, 2026 at 12:21:56AM +0100, Tomasz Lis wrote:
>>> When a context is being created during save/restore, the LRC creation
>>> needs to wait for GGTT address space to be shifted. But it also needs
>>> to have fixed default LRCs. This is mandatory to avoid the situation
>>> where LRC will be created based on data from before the fixups, but
>>> reference within exec queue will be set too late for fixups.
>>>
>>> This fixes an issue where contexts created during save/restore have
>>> a large chance of having one unfixed LRC, due to the xe_lrc_create()
>>> being synced for equal start to race with default LRC fixups.
>>>
>>> Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
>> This is better than what is in place, so...
>> Reviewed-by: Matthew Brost <matthew.brost@intel.com>
> A little quick on this RB, see my comment here [1].
>
> [1] https://patchwork.freedesktop.org/patch/705610/?series=161287&rev=2#comment_1298253
ack
>
>> But I think we need to close on why my suggestion in the previous rev
>> isn't fixing the issue (off list discussion). If we go this series, then
> We still need to figure out why my previous suggestion doesn't work.

Right. Testing this is even harder than I expected though. Not only each 
verification required 1000+ runs, but I already confirmed that there is 
more than one place within `xe_lrc_create()` which causes an issue if 
not protected by the atomic..

We need to, but this may take some time.

-Tomasz

>> my RB holds for future revs.
>>
>> Matt
>>
>>> ---
>>>   drivers/gpu/drm/xe/xe_exec_queue.c        |  2 +-
>>>   drivers/gpu/drm/xe/xe_gt_sriov_vf.c       | 24 +++++++++++------------
>>>   drivers/gpu/drm/xe/xe_gt_sriov_vf.h       |  2 +-
>>>   drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h |  4 ++--
>>>   4 files changed, 15 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
>>> index e9396ad3390a..6eb561086e1c 100644
>>> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
>>> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
>>> @@ -309,7 +309,7 @@ static int __xe_exec_queue_init(struct xe_exec_queue *q, u32 exec_queue_flags)
>>>   	for (i = 0; i < q->width; ++i) {
>>>   		struct xe_lrc *lrc;
>>>   
>>> -		xe_gt_sriov_vf_wait_valid_ggtt(q->gt);
>>> +		xe_gt_sriov_vf_wait_valid_default_lrc(q->gt);
>>>   		lrc = xe_lrc_create(q->hwe, q->vm, q->replay_state,
>>>   				    xe_lrc_ring_size(), q->msix_vec, flags);
>>>   		if (IS_ERR(lrc)) {
>>> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
>>> index 527ded3c9c22..5ce06031018d 100644
>>> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
>>> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf.c
>>> @@ -536,12 +536,6 @@ static int vf_get_ggtt_info(struct xe_gt *gt)
>>>   	 */
>>>   	xe_ggtt_shift_nodes(tile->mem.ggtt, start);
>>>   
>>> -	if (xe_sriov_vf_migration_supported(gt_to_xe(gt))) {
>>> -		WRITE_ONCE(gt->sriov.vf.migration.ggtt_need_fixes, false);
>>> -		smp_wmb();	/* Ensure above write visible before wake */
>>> -		wake_up_all(&gt->sriov.vf.migration.wq);
>>> -	}
>>> -
>>>   	return 0;
>>>   }
>>>   
>>> @@ -844,6 +838,10 @@ static void xe_gt_sriov_vf_default_lrcs_hwsp_rebase(struct xe_gt *gt)
>>>   
>>>   	for_each_hw_engine(hwe, gt, id)
>>>   		xe_default_lrc_update_memirq_regs_with_address(hwe);
>>> +
>>> +	WRITE_ONCE(gt->sriov.vf.migration.default_lrcs_need_fixes, false);
>>> +	smp_wmb();	/* Ensure above write visible before wake */
>>> +	wake_up_all(&gt->sriov.vf.migration.wq);
> Then with [1], move this wakeup to vf_post_migration_fixups after all fixups.
>
> Matt
>
>>>   }
>>>   
>>>   static void vf_start_migration_recovery(struct xe_gt *gt)
>>> @@ -858,7 +856,7 @@ static void vf_start_migration_recovery(struct xe_gt *gt)
>>>   	    !gt->sriov.vf.migration.recovery_teardown) {
>>>   		gt->sriov.vf.migration.recovery_queued = true;
>>>   		WRITE_ONCE(gt->sriov.vf.migration.recovery_inprogress, true);
>>> -		WRITE_ONCE(gt->sriov.vf.migration.ggtt_need_fixes, true);
>>> +		WRITE_ONCE(gt->sriov.vf.migration.default_lrcs_need_fixes, true);
>>>   		smp_wmb();	/* Ensure above writes visible before wake */
>>>   
>>>   		xe_guc_ct_wake_waiters(&gt->uc.guc.ct);
>>> @@ -1303,7 +1301,7 @@ static void vf_post_migration_abort(struct xe_gt *gt)
>>>   {
>>>   	spin_lock_irq(&gt->sriov.vf.migration.lock);
>>>   	WRITE_ONCE(gt->sriov.vf.migration.recovery_inprogress, false);
>>> -	WRITE_ONCE(gt->sriov.vf.migration.ggtt_need_fixes, false);
>>> +	WRITE_ONCE(gt->sriov.vf.migration.default_lrcs_need_fixes, false);
>>>   	spin_unlock_irq(&gt->sriov.vf.migration.lock);
>>>   
>>>   	wake_up_all(&gt->sriov.vf.migration.wq);
>>> @@ -1499,7 +1497,7 @@ bool xe_gt_sriov_vf_recovery_pending(struct xe_gt *gt)
>>>   	return READ_ONCE(gt->sriov.vf.migration.recovery_inprogress);
>>>   }
>>>   
>>> -static bool vf_valid_ggtt(struct xe_gt *gt)
>>> +static bool vf_valid_default_lrc(struct xe_gt *gt)
>>>   {
>>>   	struct xe_memirq *memirq = &gt_to_tile(gt)->memirq;
>>>   	bool irq_pending = xe_device_uses_memirq(gt_to_xe(gt)) &&
>>> @@ -1507,17 +1505,17 @@ static bool vf_valid_ggtt(struct xe_gt *gt)
>>>   
>>>   	xe_gt_assert(gt, IS_SRIOV_VF(gt_to_xe(gt)));
>>>   
>>> -	if (irq_pending || READ_ONCE(gt->sriov.vf.migration.ggtt_need_fixes))
>>> +	if (irq_pending || READ_ONCE(gt->sriov.vf.migration.default_lrcs_need_fixes))
>>>   		return false;
>>>   
>>>   	return true;
>>>   }
>>>   
>>>   /**
>>> - * xe_gt_sriov_vf_wait_valid_ggtt() - VF wait for valid GGTT addresses
>>> + * xe_gt_sriov_vf_wait_valid_default_lrc() - wait for valid GGTT refs in default LRCs
>>>    * @gt: the &xe_gt
>>>    */
>>> -void xe_gt_sriov_vf_wait_valid_ggtt(struct xe_gt *gt)
>>> +void xe_gt_sriov_vf_wait_valid_default_lrc(struct xe_gt *gt)
>>>   {
>>>   	int ret;
>>>   
>>> @@ -1526,7 +1524,7 @@ void xe_gt_sriov_vf_wait_valid_ggtt(struct xe_gt *gt)
>>>   		return;
>>>   
>>>   	ret = wait_event_interruptible_timeout(gt->sriov.vf.migration.wq,
>>> -					       vf_valid_ggtt(gt),
>>> +					       vf_valid_default_lrc(gt),
>>>   					       HZ * 5);
>>>   	xe_gt_WARN_ON(gt, !ret);
>>>   }
>>> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf.h b/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
>>> index 7d97189c2d3d..70232dc38f9a 100644
>>> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
>>> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf.h
>>> @@ -39,6 +39,6 @@ void xe_gt_sriov_vf_print_config(struct xe_gt *gt, struct drm_printer *p);
>>>   void xe_gt_sriov_vf_print_runtime(struct xe_gt *gt, struct drm_printer *p);
>>>   void xe_gt_sriov_vf_print_version(struct xe_gt *gt, struct drm_printer *p);
>>>   
>>> -void xe_gt_sriov_vf_wait_valid_ggtt(struct xe_gt *gt);
>>> +void xe_gt_sriov_vf_wait_valid_default_lrc(struct xe_gt *gt);
>>>   
>>>   #endif
>>> diff --git a/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h b/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
>>> index 4ef881b9b662..8be181bf3cf3 100644
>>> --- a/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
>>> +++ b/drivers/gpu/drm/xe/xe_gt_sriov_vf_types.h
>>> @@ -73,8 +73,8 @@ struct xe_gt_sriov_vf_migration {
>>>   	bool recovery_queued;
>>>   	/** @recovery_inprogress: VF post migration recovery in progress */
>>>   	bool recovery_inprogress;
>>> -	/** @ggtt_need_fixes: VF GGTT needs fixes */
>>> -	bool ggtt_need_fixes;
>>> +	/** @default_lrcs_need_fixes: GGTT refs within default LRCs need fixes */
>>> +	bool default_lrcs_need_fixes;
>>>   };
>>>   
>>>   /**
>>> -- 
>>> 2.25.1
>>>