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

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

On Fri, Oct 24, 2025 at 12:55:23PM -0600, Summers, Stuart wrote:
> 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?
> 

I'd think this matters as it is a software init.

> > +       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.
> 

Yes, this should be drmm.

Matt

> 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;
> >  }
> >  
> >  /**
>