Re: [PATCH 02/11] drm/xe: Implement xe_pagefault_init

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

On Thu, 2025-08-28 at 13:14 -0700, Matthew Brost wrote:
> On Thu, Aug 28, 2025 at 02:10:02PM -0600, Summers, Stuart wrote:
> > On Tue, 2025-08-05 at 23:22 -0700, Matthew Brost wrote:
> > > Create pagefault queues and initialize them.
> > > 
> > > 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 |  6 ++
> > >  drivers/gpu/drm/xe/xe_pagefault.c    | 93
> > > +++++++++++++++++++++++++++-
> > >  3 files changed, 102 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/xe/xe_device.c
> > > b/drivers/gpu/drm/xe/xe_device.c
> > > index 57edbc63da6f..c7c8aee03841 100644
> > > --- a/drivers/gpu/drm/xe/xe_device.c
> > > +++ b/drivers/gpu/drm/xe/xe_device.c
> > > @@ -50,6 +50,7 @@
> > >  #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"
> > > @@ -890,6 +891,10 @@ int xe_device_probe(struct xe_device *xe)
> > >         if (err)
> > >                 return err;
> > >  
> > > +       err = xe_pagefault_init(xe);
> > > +       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 01e8fa0d2f9f..6aa119026ce9 100644
> > > --- a/drivers/gpu/drm/xe/xe_device_types.h
> > > +++ b/drivers/gpu/drm/xe/xe_device_types.h
> > > @@ -17,6 +17,7 @@
> > >  #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"
> > > @@ -394,6 +395,11 @@ 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;
> > > +#define XE_PAGEFAULT_QUEUE_COUNT       4
> > > +               /** @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 3ce0e8d74b9d..14304c41eb23 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"
> > >  
> > > @@ -19,6 +23,71 @@
> > >   * with a single shared consumer.
> > >   */
> > >  
> > > +static int xe_pagefault_entry_size(void)
> > > +{
> > > +       return roundup_pow_of_two(sizeof(struct xe_pagefault));
> > 
> > And here, it would be nice if you could add a brief comment that
> > this
> > assumes the size of struct xe_pagefault aligns to the hardware
> > requirements.
> > 
> 
> It is actually not a hardware thing, it the pagefault queue
> management
> code (software) where the logic breaks if we are not doing everything
> on
> pow2 boundaries. Ofc, this isn't a strick requirement, rather it just
> makes the code simplier.
> 
> I can add a comment around this.

Ok got it. Yeah that would be helpful here I agree.

Thanks,
Stuart

> 
> Matt
> 
> > Thanks,
> > Stuart
> > 
> > > +}
> > > +
> > > +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);
> > > +       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
> > > @@ -29,8 +98,28 @@
> > >   */
> > >  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;
> > >  }
> > >  
> > >  /**
> >