Re: [PATCH v2] drm/xe/guc: Guard page-fault ack with runtime PM check

["Ghimiray, Himal Prasad" <himal.prasad.ghimiray@intel.com>]

On 04-09-2026 14:00, Matthew Brost wrote:
> On Fri, Sep 04, 2026 at 01:35:06PM +0530, Varun Gupta wrote:
>> During VM teardown, the VM's runtime PM reference is dropped
>> asynchronously, allowing the device to autosuspend while stale page
>> faults belonging to the now-dead VM are still queued. When the
>> page-fault worker later tries to ack one of these, it calls into
>> guc_ct_send_locked() on an already-suspended device, tripping:
>>
>>    Assertion `!xe_pm_runtime_suspended(xe)` failed!
>>    WARNING at xe_device.c:1267 xe_device_assert_mem_access+0x11c/0x140 [xe]
>>
>> A live VM/exec queue always holds a PM reference while it has
>> outstanding work, so if the device is suspended at ack time, the
>> owning context is already gone and the fault is stale.
>>
>> Take a runtime PM reference across the entire page-fault ack batch
>> preventing mid-batch suspends.
>>
>> v2:
>>   - Hold PM ref across the entire batch (begin/end) instead of per-ack.
>>     This prevents the device from autosuspending mid-batch, which would
>>     leave write_only acks written but the end flush skipped, and skip
>>     counter++, desyncing the cadence check.(Himal)
>>   - Add a comment explaining stale faults.(Himal)
>>
> 
> I'd guard the entire page fault fault handler with PM a ref rather than
> the ack part.
> 
> e.g. At the very top of xe_pagefault_queue_work:
> 
> guard(xe_pm_runtime)(xe);

+1
> 
> Matt
> 
>> Fixes: f289f7807119 ("drm/xe: Add xe_guc_pagefault layer")
>> Reported-by: Szymon Markiewicz <szymon.markiewicz@intel.com>
>> Signed-off-by: Varun Gupta <varun.gupta@intel.com>
>> ---
>>   drivers/gpu/drm/xe/xe_guc_pagefault.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_guc_pagefault.c b/drivers/gpu/drm/xe/xe_guc_pagefault.c
>> index 8f8210a732e9..9c9cd6e056fb 100644
>> --- a/drivers/gpu/drm/xe/xe_guc_pagefault.c
>> +++ b/drivers/gpu/drm/xe/xe_guc_pagefault.c
>> @@ -9,12 +9,21 @@
>>   #include "xe_guc_pagefault.h"
>>   #include "xe_pagefault.h"
>>   #include "xe_pagefault_types.h"
>> +#include "xe_pm.h"
>>   
>>   #define XE_GUC_PAGEFAULT_FLUSH_PERIOD	BIT(4)	/* Sixteen */
>>   
>>   static void guc_ack_fault_begin(void *private)
>>   {
>>   	struct xe_guc *guc = private;
>> +	struct xe_device *xe = guc_to_xe(guc);
>> +
>> +	/*
>> +	 * Live VMs hold a PM ref, so faults during suspend are stale.
>> +	 * Hold a PM ref across the entire batch to safely drain them
>> +	 * and prevent mid-batch autosuspend from desyncing CT flushes.
>> +	 */
>> +	xe_pm_runtime_get(xe);
>>   
>>   	xe_guc_ct_lock(&guc->ct);
>>   
>> @@ -62,10 +71,13 @@ static void guc_ack_fault(struct xe_pagefault *pf, int err)
>>   static void guc_ack_fault_end(void *private)
>>   {
>>   	struct xe_guc *guc = private;
>> +	struct xe_device *xe = guc_to_xe(guc);
>>   
>>   	if ((guc->pagefault_ack_counter & (XE_GUC_PAGEFAULT_FLUSH_PERIOD - 1)) != 1)
>>   		xe_guc_ct_send_flush(&guc->ct);
>>   	xe_guc_ct_unlock(&guc->ct);
>> +
>> +	xe_pm_runtime_put(xe);
>>   }
>>   
>>   static const struct xe_pagefault_ops guc_pagefault_ops = {
>> -- 
>> 2.43.0
>>