Re: [PATCH v2 2/7] drm/xe: Implement xe_pagefault_init

["Summers, Stuart" <stuart.summers@intel.com>]

On Fri, 2025-10-24 at 11:04 -0700, Matthew Brost wrote:
> Create pagefault queues and initialize them.
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> 
> ---
> v2:
>  - Fix kernel doc + add comment for number PF queue (Francois)
> ---
>  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 5f6a412b571c..f4261a461ddb 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"
> @@ -904,6 +905,10 @@ int xe_device_probe(struct xe_device *xe)
>         if (err)
>                 return err;
>  
> +       err = xe_pagefault_init(xe);

Before we were calling this with the GT init. Should we move this above
there? Or otherwise why is this later?

> +       if (err)
> +               return err;
> +
>         xe_nvm_init(xe);
>  
>         err = xe_heci_gsc_init(xe);
> diff --git a/drivers/gpu/drm/xe/xe_device_types.h
> b/drivers/gpu/drm/xe/xe_device_types.h
> index 6a62b520f5b5..a578781cc28b 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..ea3813704242 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));
> +}
> +
> +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);
> +
> +       pf_queue->data = devm_kzalloc(xe->drm.dev, pf_queue->size,
> GFP_KERNEL);

Why devm here instead of drmm? I see we're using drmm for things like
the mutex init in xe_devcoredump_init() which happens before this.

Thanks,
Stuart

> +       if (!pf_queue->data)
> +               return -ENOMEM;
> +
> +       spin_lock_init(&pf_queue->lock);
> +       INIT_WORK(&pf_queue->worker, xe_pagefault_queue_work);
> +
> +       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;
>  }
>  
>  /**