Re: [PATCH v4 11/12] drm/xe: Add context-based invalidation to GuC TLB invalidation backend

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

On Mon, 2026-01-12 at 18:52 -0800, Matthew Brost wrote:
> Introduce context-based invalidation support to the GuC TLB
> invalidation
> backend. This is implemented by iterating over each exec queue per GT
> within a VM, skipping inactive queues, and issuing a context-based
> (GuC
> ID) H2G TLB invalidation. All H2G messages, except the final one, are
> sent with an invalid seqno, which the G2H handler drops to ensure the
> TLB invalidation fence is only signaled once all H2G messages are
> completed.
> 
> A watermark mechanism is also added to switch between context-based
> TLB
> invalidations and full device-wide invalidations, as the return on
> investment for context-based invalidation diminishes when many exec
> queues are mapped.
> 
> v2:
>  - Fix checkpatch warnings
> v3:
>  - Rebase on PRL
>  - Use ref counting to avoid racing with deregisters
> v4:
>  - Extra braces (Stuart)
>  - Use per GT list (CI)
>  - Reorder put
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_guc_tlb_inval.c | 145
> +++++++++++++++++++++++++-
>  1 file changed, 141 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> b/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> index 070d2e2cb7c9..ced58f46f846 100644
> --- a/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> +++ b/drivers/gpu/drm/xe/xe_guc_tlb_inval.c
> @@ -6,15 +6,19 @@
>  #include "abi/guc_actions_abi.h"
>  
>  #include "xe_device.h"
> +#include "xe_exec_queue.h"
> +#include "xe_exec_queue_types.h"
>  #include "xe_gt_stats.h"
>  #include "xe_gt_types.h"
>  #include "xe_guc.h"
>  #include "xe_guc_ct.h"
> +#include "xe_guc_exec_queue_types.h"
>  #include "xe_guc_tlb_inval.h"
>  #include "xe_force_wake.h"
>  #include "xe_mmio.h"
>  #include "xe_sa.h"
>  #include "xe_tlb_inval.h"
> +#include "xe_vm.h"
>  
>  #include "regs/xe_guc_regs.h"
>  
> @@ -156,10 +160,16 @@ static int send_tlb_inval_ppgtt(struct xe_guc
> *guc, u32 seqno, u64 start,
>  {
>  #define MAX_TLB_INVALIDATION_LEN       7
>         struct xe_gt *gt = guc_to_gt(guc);
> +       struct xe_device *xe = guc_to_xe(guc);
>         u32 action[MAX_TLB_INVALIDATION_LEN];
>         u64 length = end - start;
>         int len = 0, err;
>  
> +       xe_gt_assert(gt, (type == XE_GUC_TLB_INVAL_PAGE_SELECTIVE &&
> +                         !xe->info.has_ctx_tlb_inval) ||
> +                    (type == XE_GUC_TLB_INVAL_PAGE_SELECTIVE_CTX &&
> +                     xe->info.has_ctx_tlb_inval));
> +
>         action[len++] = XE_GUC_ACTION_TLB_INVALIDATION;
>         action[len++] = !prl_sa ? seqno :
> TLB_INVALIDATION_SEQNO_INVALID;
>         if (!gt_to_xe(gt)->info.has_range_tlb_inval ||
> @@ -168,9 +178,11 @@ static int send_tlb_inval_ppgtt(struct xe_guc
> *guc, u32 seqno, u64 start,
>         } else {
>                 u64 normalize_len = normalize_invalidation_range(gt,
> &start,
>                                                                 
> &end);
> +               bool need_flush = !prl_sa &&
> +                       seqno != TLB_INVALIDATION_SEQNO_INVALID;
>  
>                 /* Flush on NULL case, Media is not required to
> modify flush due to no PPC so NOP */
> -               action[len++] = MAKE_INVAL_OP_FLUSH(type, !prl_sa);
> +               action[len++] = MAKE_INVAL_OP_FLUSH(type,
> need_flush);
>                 action[len++] = id;
>                 action[len++] = lower_32_bits(start);
>                 action[len++] = upper_32_bits(start);
> @@ -181,8 +193,10 @@ static int send_tlb_inval_ppgtt(struct xe_guc
> *guc, u32 seqno, u64 start,
>  #undef MAX_TLB_INVALIDATION_LEN
>  
>         err = send_tlb_inval(guc, action, len);
> -       if (!err && prl_sa)
> +       if (!err && prl_sa) {
> +               xe_gt_assert(gt, seqno !=
> TLB_INVALIDATION_SEQNO_INVALID);
>                 err = send_page_reclaim(guc, seqno,
> xe_sa_bo_gpu_addr(prl_sa));
> +       }
>         return err;
>  }
>  
> @@ -201,6 +215,114 @@ static int send_tlb_inval_asid_ppgtt(struct
> xe_tlb_inval *tlb_inval, u32 seqno,
>                                     XE_GUC_TLB_INVAL_PAGE_SELECTIVE,
> prl_sa);
>  }
>  
> +static int send_tlb_inval_ctx_ppgtt(struct xe_tlb_inval *tlb_inval,
> u32 seqno,
> +                                   u64 start, u64 end, u32 asid,
> +                                   struct drm_suballoc *prl_sa)
> +{
> +       struct xe_guc *guc = tlb_inval->private;
> +       struct xe_device *xe = guc_to_xe(guc);
> +       struct xe_exec_queue *q, *next, *last_q = NULL;
> +       struct xe_vm *vm;
> +       LIST_HEAD(tlb_inval_list);
> +       int err = 0, id = guc_to_gt(guc)->info.id;
> +
> +       lockdep_assert_held(&tlb_inval->seqno_lock);
> +
> +       if (xe->info.force_execlist)
> +               return -ECANCELED;
> +
> +       vm = xe_device_asid_to_vm(xe, asid);
> +       if (IS_ERR(vm))
> +               return PTR_ERR(vm);
> +
> +       down_read(&vm->exec_queues.lock);
> +
> +       /*
> +        * XXX: Randomly picking a threshold for now. This will need
> to be
> +        * tuned based on expected UMD queue counts and performance
> profiling.
> +        */
> +#define EXEC_QUEUE_COUNT_FULL_THRESHOLD        8
> +       if (vm->exec_queues.count[id] >=
> EXEC_QUEUE_COUNT_FULL_THRESHOLD) {
> +               u32 action[] = {
> +                       XE_GUC_ACTION_TLB_INVALIDATION,
> +                       seqno,
> +                       MAKE_INVAL_OP(XE_GUC_TLB_INVAL_FULL),
> +               };
> +
> +               err = send_tlb_inval(guc, action,
> ARRAY_SIZE(action));
> +               goto err_unlock;
> +       }
> +#undef EXEC_QUEUE_COUNT_FULL_THRESHOLD
> +
> +       /*
> +        * Move exec queues to a temporary list to issue
> invalidations. The exec
> +        * queue must active and a reference must be taken to prevent
> concurrent
> +        * deregistrations.
> +        *
> +        * List modification is safe because we hold 'vm-
> >exec_queues.lock' for
> +        * reading, which prevents external modifications. Using a
> per-GT list
> +        * is also safe since 'tlb_inval->seqno_lock' ensures no
> other GT users
> +        * can enter this code path.
> +        */
> +       list_for_each_entry_safe(q, next, &vm->exec_queues.list[id],
> +                                vm_exec_queue_link) {
> +               if (q->ops->active(q) &&
> xe_exec_queue_get_unless_zero(q)) {
> +                       last_q = q;
> +                       list_move_tail(&q->vm_exec_queue_link,
> &tlb_inval_list);

It would be nice if we could consolidate this into a single list
instead of moving things around like this, but I realize this makes it
easier to track the last active queue so no issue...

I don't see anything blocking us from deregistering a queue though
after it has been moved to the tlb_inval_list here. Should we add that
seqno_lock in the register/deregister routines to be safe? Or maybe
block until tlb_inval_list is empty? Or if I'm missing it otherwise,
how are you preventing the deregistration after this is on the list?

Thanks,
Stuart

> +               }
> +       }
> +
> +       if (!last_q) {
> +               /*
> +                * We can't break fence ordering for TLB invalidation
> jobs, if
> +                * TLB invalidations are inflight issue a dummy
> invalidation to
> +                * maintain ordering. Nor can we move safely the
> seqno_recv when
> +                * returning -ECANCELED if TLB invalidations are in
> flight. Use
> +                * GGTT invalidation as dummy invalidation given ASID
> +                * invalidations are unsupported here.
> +                */
> +               if (xe_tlb_inval_idle(tlb_inval))
> +                       err = -ECANCELED;
> +               else
> +                       err = send_tlb_inval_ggtt(tlb_inval, seqno);
> +               goto err_unlock;
> +       }
> +
> +       list_for_each_entry_safe(q, next, &tlb_inval_list,
> vm_exec_queue_link) {
> +               struct drm_suballoc *__prl_sa = NULL;
> +               int __seqno = TLB_INVALIDATION_SEQNO_INVALID;
> +               u32 type = XE_GUC_TLB_INVAL_PAGE_SELECTIVE_CTX;
> +
> +               xe_assert(xe, q->vm == vm);
> +
> +               if (err)
> +                       goto unref;
> +
> +               if (last_q == q) {
> +                       __prl_sa = prl_sa;
> +                       __seqno = seqno;
> +               }
> +
> +               err = send_tlb_inval_ppgtt(guc, __seqno, start, end,
> +                                          q->guc->id, type,
> __prl_sa);
> +
> +unref:
> +               /*
> +                * Must always return exec queue to original list /
> drop
> +                * reference
> +                */
> +               list_move_tail(&q->vm_exec_queue_link,
> +                              &vm->exec_queues.list[id]);
> +               xe_exec_queue_put(q);
> +       }
> +
> +err_unlock:
> +       up_read(&vm->exec_queues.lock);
> +       xe_vm_put(vm);
> +
> +       return err;
> +}
> +
>  static bool tlb_inval_initialized(struct xe_tlb_inval *tlb_inval)
>  {
>         struct xe_guc *guc = tlb_inval->private;
> @@ -228,7 +350,7 @@ static long tlb_inval_timeout_delay(struct
> xe_tlb_inval *tlb_inval)
>         return hw_tlb_timeout + 2 * delay;
>  }
>  
> -static const struct xe_tlb_inval_ops guc_tlb_inval_ops = {
> +static const struct xe_tlb_inval_ops guc_tlb_inval_asid_ops = {
>         .all = send_tlb_inval_all,
>         .ggtt = send_tlb_inval_ggtt,
>         .ppgtt = send_tlb_inval_asid_ppgtt,
> @@ -237,6 +359,15 @@ static const struct xe_tlb_inval_ops
> guc_tlb_inval_ops = {
>         .timeout_delay = tlb_inval_timeout_delay,
>  };
>  
> +static const struct xe_tlb_inval_ops guc_tlb_inval_ctx_ops = {
> +       .ggtt = send_tlb_inval_ggtt,
> +       .all = send_tlb_inval_all,
> +       .ppgtt = send_tlb_inval_ctx_ppgtt,
> +       .initialized = tlb_inval_initialized,
> +       .flush = tlb_inval_flush,
> +       .timeout_delay = tlb_inval_timeout_delay,
> +};
> +
>  /**
>   * xe_guc_tlb_inval_init_early() - Init GuC TLB invalidation early
>   * @guc: GuC object
> @@ -248,8 +379,14 @@ static const struct xe_tlb_inval_ops
> guc_tlb_inval_ops = {
>  void xe_guc_tlb_inval_init_early(struct xe_guc *guc,
>                                  struct xe_tlb_inval *tlb_inval)
>  {
> +       struct xe_device *xe = guc_to_xe(guc);
> +
>         tlb_inval->private = guc;
> -       tlb_inval->ops = &guc_tlb_inval_ops;
> +
> +       if (xe->info.has_ctx_tlb_inval)
> +               tlb_inval->ops = &guc_tlb_inval_ctx_ops;
> +       else
> +               tlb_inval->ops = &guc_tlb_inval_asid_ops;
>  }
>  
>  /**