Re: [PATCH v3] drm/xe: Guard page-fault worker with runtime PM check

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Sep 04, 2026 at 02:46:57PM +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 pagefault
> queue worker to safely deliver acks for torn-down VMs.
> 
> v3:
>  - Move PM ref to the generic xe_pagefault_queue_work using
>    guard(xe_pm_runtime)(xe) instead of tracking it in the GuC
>    backend(Matt Brost).
> 
> 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)
> 
> Fixes: f289f7807119 ("drm/xe: Add xe_guc_pagefault layer")
> Reported-by: Szymon Markiewicz <szymon.markiewicz@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> Signed-off-by: Varun Gupta <varun.gupta@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_pagefault.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pagefault.c b/drivers/gpu/drm/xe/xe_pagefault.c
> index 2e415995f067..3e8e8f7f5f40 100644
> --- a/drivers/gpu/drm/xe/xe_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_pagefault.c
> @@ -17,6 +17,7 @@
>  #include "xe_log.h"
>  #include "xe_pagefault.h"
>  #include "xe_pagefault_types.h"
> +#include "xe_pm.h"
>  #include "xe_svm.h"
>  #include "xe_trace_bo.h"
>  #include "xe_vm.h"
> @@ -604,6 +605,13 @@ static void xe_pagefault_queue_work(struct work_struct *w)
>  	u64 cache_start = XE_PAGEFAULT_CACHE_START_INVALID, cache_end = 0;
>  	u32 cache_asid = 0;
>  
> +	/*
> +	 * A live VM holds a PM reference, but a torn-down VM does not.
> +	 * Guard the entire worker loop to safely drain stale faults and
> +	 * prevent autosuspends from desyncing batched CT flushes.
> +	 */
> +	guard(xe_pm_runtime)(xe);
> +
>  #define USM_QUEUE_MAX_RUNTIME_MS      20
>  	threshold = jiffies + msecs_to_jiffies(USM_QUEUE_MAX_RUNTIME_MS);
>  
> -- 
> 2.43.0
>