Re: [PATCH v4 2/7] drm/xe: Implement xe_pagefault_init

[Francois Dugast <francois.dugast@intel.com>]

On Fri, Oct 31, 2025 at 09:54:11AM -0700, Matthew Brost wrote:
> Create pagefault queues and initialize them.
> 
> v2:
>  - Fix kernel doc + add comment for number PF queue (Francois)
> v4:
>  - Move init after GT init (CI, Francois)
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_device.c       |  5 ++
>  drivers/gpu/drm/xe/xe_device_types.h | 11 ++++
>  drivers/gpu/drm/xe/xe_pagefault.c    | 93 +++++++++++++++++++++++++++-
>  3 files changed, 107 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
> index 47f5391ad8e9..4238ba28fac7 100644
> --- a/drivers/gpu/drm/xe/xe_device.c
> +++ b/drivers/gpu/drm/xe/xe_device.c
> @@ -52,6 +52,7 @@
>  #include "xe_nvm.h"
>  #include "xe_oa.h"
>  #include "xe_observation.h"
> +#include "xe_pagefault.h"
>  #include "xe_pat.h"
>  #include "xe_pcode.h"
>  #include "xe_pm.h"
> @@ -896,6 +897,10 @@ int xe_device_probe(struct xe_device *xe)
>  			return err;
>  	}
>  
> +	err = xe_pagefault_init(xe);
> +	if (err)
> +		return err;
> +
>  	if (xe->tiles->media_gt &&
>  	    XE_GT_WA(xe->tiles->media_gt, 15015404425_disable))
>  		XE_DEVICE_WA_DISABLE(xe, 15015404425);
> diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
> index af0ce275b032..7baf15f51575 100644
> --- a/drivers/gpu/drm/xe/xe_device_types.h
> +++ b/drivers/gpu/drm/xe/xe_device_types.h
> @@ -18,6 +18,7 @@
>  #include "xe_lmtt_types.h"
>  #include "xe_memirq_types.h"
>  #include "xe_oa_types.h"
> +#include "xe_pagefault_types.h"
>  #include "xe_platform_types.h"
>  #include "xe_pmu_types.h"
>  #include "xe_pt_types.h"
> @@ -418,6 +419,16 @@ struct xe_device {
>  		u32 next_asid;
>  		/** @usm.lock: protects UM state */
>  		struct rw_semaphore lock;
> +		/** @usm.pf_wq: page fault work queue, unbound, high priority */
> +		struct workqueue_struct *pf_wq;
> +		/*
> +		 * We pick 4 here because, in the current implementation, it
> +		 * yields the best bandwidth utilization of the kernel paging
> +		 * engine.
> +		 */
> +#define XE_PAGEFAULT_QUEUE_COUNT	4
> +		/** @usm.pf_queue: Page fault queues */
> +		struct xe_pagefault_queue pf_queue[XE_PAGEFAULT_QUEUE_COUNT];
>  	} usm;
>  
>  	/** @pinned: pinned BO state */
> diff --git a/drivers/gpu/drm/xe/xe_pagefault.c b/drivers/gpu/drm/xe/xe_pagefault.c
> index d509a80cb1f3..43b26e7d090a 100644
> --- a/drivers/gpu/drm/xe/xe_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_pagefault.c
> @@ -3,6 +3,10 @@
>   * Copyright © 2025 Intel Corporation
>   */
>  
> +#include <drm/drm_managed.h>
> +
> +#include "xe_device.h"
> +#include "xe_gt_types.h"
>  #include "xe_pagefault.h"
>  #include "xe_pagefault_types.h"
>  
> @@ -21,6 +25,71 @@
>   * xe_pagefault.c implements the consumer layer.
>   */
>  
> +static int xe_pagefault_entry_size(void)
> +{
> +	return roundup_pow_of_two(sizeof(struct xe_pagefault));

It seems this is missing:
https://patchwork.freedesktop.org/patch/667318/?series=152565&rev=1#comment_1230914

With that:
	Reviewed-by: Francois Dugast <francois.dugast@intel.com>

> +}
> +
> +static void xe_pagefault_queue_work(struct work_struct *w)
> +{
> +	/* TODO: Implement */
> +}
> +
> +static int xe_pagefault_queue_init(struct xe_device *xe,
> +				   struct xe_pagefault_queue *pf_queue)
> +{
> +	struct xe_gt *gt;
> +	int total_num_eus = 0;
> +	u8 id;
> +
> +	for_each_gt(gt, xe, id) {
> +		xe_dss_mask_t all_dss;
> +		int num_dss, num_eus;
> +
> +		bitmap_or(all_dss, gt->fuse_topo.g_dss_mask,
> +			  gt->fuse_topo.c_dss_mask, XE_MAX_DSS_FUSE_BITS);
> +
> +		num_dss = bitmap_weight(all_dss, XE_MAX_DSS_FUSE_BITS);
> +		num_eus = bitmap_weight(gt->fuse_topo.eu_mask_per_dss,
> +					XE_MAX_EU_FUSE_BITS) * num_dss;
> +
> +		total_num_eus += num_eus;
> +	}
> +
> +	xe_assert(xe, total_num_eus);
> +
> +	/*
> +	 * user can issue separate page faults per EU and per CS
> +	 *
> +	 * XXX: Multiplier required as compute UMD are getting PF queue errors
> +	 * without it. Follow on why this multiplier is required.
> +	 */
> +#define PF_MULTIPLIER	8
> +	pf_queue->size = (total_num_eus + XE_NUM_HW_ENGINES) *
> +		xe_pagefault_entry_size() * PF_MULTIPLIER;
> +	pf_queue->size = roundup_pow_of_two(pf_queue->size);
> +#undef PF_MULTIPLIER
> +
> +	drm_dbg(&xe->drm, "xe_pagefault_entry_size=%d, total_num_eus=%d, pf_queue->size=%u",
> +		xe_pagefault_entry_size(), total_num_eus, pf_queue->size);
> +
> +	spin_lock_init(&pf_queue->lock);
> +	INIT_WORK(&pf_queue->worker, xe_pagefault_queue_work);
> +
> +	pf_queue->data = drmm_kzalloc(&xe->drm, pf_queue->size, GFP_KERNEL);
> +	if (!pf_queue->data)
> +		return -ENOMEM;
> +
> +	return 0;
> +}
> +
> +static void xe_pagefault_fini(void *arg)
> +{
> +	struct xe_device *xe = arg;
> +
> +	destroy_workqueue(xe->usm.pf_wq);
> +}
> +
>  /**
>   * xe_pagefault_init() - Page fault init
>   * @xe: xe device instance
> @@ -31,8 +100,28 @@
>   */
>  int xe_pagefault_init(struct xe_device *xe)
>  {
> -	/* TODO - implement */
> -	return 0;
> +	int err, i;
> +
> +	if (!xe->info.has_usm)
> +		return 0;
> +
> +	xe->usm.pf_wq = alloc_workqueue("xe_page_fault_work_queue",
> +					WQ_UNBOUND | WQ_HIGHPRI,
> +					XE_PAGEFAULT_QUEUE_COUNT);
> +	if (!xe->usm.pf_wq)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < XE_PAGEFAULT_QUEUE_COUNT; ++i) {
> +		err = xe_pagefault_queue_init(xe, xe->usm.pf_queue + i);
> +		if (err)
> +			goto err_out;
> +	}
> +
> +	return devm_add_action_or_reset(xe->drm.dev, xe_pagefault_fini, xe);
> +
> +err_out:
> +	destroy_workqueue(xe->usm.pf_wq);
> +	return err;
>  }
>  
>  /**
> -- 
> 2.34.1
>