[PATCH v2] drm/xe: Rework eviction rejection of bound external bos
Matthew Brost
matthew.brost at intel.com
Wed May 28 15:50:37 UTC 2025
On Wed, May 28, 2025 at 09:37:40AM +0200, Thomas Hellström wrote:
> On Tue, 2025-05-27 at 11:57 -0700, Matthew Brost wrote:
> > On Mon, May 26, 2025 at 06:16:32PM +0200, Thomas Hellström wrote:
> > > For preempt_fence mode VM's we're rejecting eviction of
> > > shared bos during VM_BIND. However, since we do this in the
> > > move() callback, we're getting an eviction failure warning from
> > > TTM. The TTM callback intended for these things is
> > > eviction_valuable().
> > >
> > > However, the latter doesn't pass in the struct ttm_operation_ctx
> > > needed to determine whether the caller needs this.
> > >
> > > Instead, attach the needed information to the vm under the
> > > vm->resv, until we've been able to update TTM to provide the
> > > needed information. And add sufficient lockdep checks to prevent
> > > misuse and races.
> > >
> > > v2:
> > > - Fix a copy-paste error in xe_vm_clear_validating()
> > >
> > > Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> > > Fixes: 0af944f0e308 ("drm/xe: Reject BO eviction if BO is bound to
> > > current VM")
> > > Cc: Oak Zeng <oak.zeng at intel.com>
> > > ---
> > > drivers/gpu/drm/xe/xe_bo.c | 46 +++++++++++++---------
> > > drivers/gpu/drm/xe/xe_vm.h | 65
> > > ++++++++++++++++++++++++++++++++
> > > drivers/gpu/drm/xe/xe_vm_types.h | 8 ++++
> > > 3 files changed, 101 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > > b/drivers/gpu/drm/xe/xe_bo.c
> > > index d99d91fe8aa9..3c48a8c5f439 100644
> > > --- a/drivers/gpu/drm/xe/xe_bo.c
> > > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > > @@ -841,21 +841,6 @@ static int xe_bo_move(struct ttm_buffer_object
> > > *ttm_bo, bool evict,
> > > goto out;
> > > }
> > >
> > > - /* Reject BO eviction if BO is bound to current VM. */
> > > - if (evict && ctx->resv) {
> > > - struct drm_gpuvm_bo *vm_bo;
> > > -
> > > - drm_gem_for_each_gpuvm_bo(vm_bo, &bo->ttm.base) {
> > > - struct xe_vm *vm = gpuvm_to_vm(vm_bo->vm);
> > > -
> > > - if (xe_vm_resv(vm) == ctx->resv &&
> > > - xe_vm_in_preempt_fence_mode(vm)) {
> > > - ret = -EBUSY;
> > > - goto out;
> > > - }
> > > - }
> > > - }
> > > -
> > > /*
> > > * Failed multi-hop where the old_mem is still marked as
> > > * TTM_PL_FLAG_TEMPORARY, should just be a dummy move.
> > > @@ -1013,6 +998,25 @@ static long xe_bo_shrink_purge(struct
> > > ttm_operation_ctx *ctx,
> > > return lret;
> > > }
> > >
> > > +static bool
> > > +xe_bo_eviction_valuable(struct ttm_buffer_object *bo, const struct
> > > ttm_place *place)
> > > +{
> > > + struct drm_gpuvm_bo *vm_bo;
> > > +
> > > + if (!ttm_bo_eviction_valuable(bo, place))
> > > + return false;
> > > +
> > > + if (!xe_bo_is_xe_bo(bo))
> > > + return true;
> > > +
> > > + drm_gem_for_each_gpuvm_bo(vm_bo, &bo->base) {
> > > + if (xe_vm_is_validating(gpuvm_to_vm(vm_bo->vm)))
> > > + return false;
> > > + }
> > > +
> > > + return true;
> > > +}
> > > +
> > > /**
> > > * xe_bo_shrink() - Try to shrink an xe bo.
> > > * @ctx: The struct ttm_operation_ctx used for shrinking.
> > > @@ -1047,7 +1051,7 @@ long xe_bo_shrink(struct ttm_operation_ctx
> > > *ctx, struct ttm_buffer_object *bo,
> > > (flags.purge && !xe_tt->purgeable))
> > > return -EBUSY;
> > >
> > > - if (!ttm_bo_eviction_valuable(bo, &place))
> > > + if (!xe_bo_eviction_valuable(bo, &place))
> > > return -EBUSY;
> > >
> > > if (!xe_bo_is_xe_bo(bo) || !xe_bo_get_unless_zero(xe_bo))
> > > @@ -1588,7 +1592,7 @@ const struct ttm_device_funcs xe_ttm_funcs =
> > > {
> > > .io_mem_pfn = xe_ttm_io_mem_pfn,
> > > .access_memory = xe_ttm_access_memory,
> > > .release_notify = xe_ttm_bo_release_notify,
> > > - .eviction_valuable = ttm_bo_eviction_valuable,
> > > + .eviction_valuable = xe_bo_eviction_valuable,
> > > .delete_mem_notify = xe_ttm_bo_delete_mem_notify,
> > > .swap_notify = xe_ttm_bo_swap_notify,
> > > };
> > > @@ -2431,6 +2435,8 @@ int xe_bo_validate(struct xe_bo *bo, struct
> > > xe_vm *vm, bool allow_res_evict)
> > > .no_wait_gpu = false,
> > > .gfp_retry_mayfail = true,
> > > };
> > > + struct pin_cookie cookie;
> > > + int ret;
> > >
> > > if (vm) {
> > > lockdep_assert_held(&vm->lock);
> > > @@ -2440,8 +2446,12 @@ int xe_bo_validate(struct xe_bo *bo, struct
> > > xe_vm *vm, bool allow_res_evict)
> > > ctx.resv = xe_vm_resv(vm);
> > > }
> > >
> > > + cookie = xe_vm_set_validating(vm, allow_res_evict);
> > > trace_xe_bo_validate(bo);
> > > - return ttm_bo_validate(&bo->ttm, &bo->placement, &ctx);
> > > + ret = ttm_bo_validate(&bo->ttm, &bo->placement, &ctx);
> > > + xe_vm_clear_validating(vm, allow_res_evict, cookie);
> > > +
> > > + return ret;
> > > }
> > >
> > > bool xe_bo_is_xe_bo(struct ttm_buffer_object *bo)
> > > diff --git a/drivers/gpu/drm/xe/xe_vm.h
> > > b/drivers/gpu/drm/xe/xe_vm.h
> > > index 99e164852f63..fe05c4f7f425 100644
> > > --- a/drivers/gpu/drm/xe/xe_vm.h
> > > +++ b/drivers/gpu/drm/xe/xe_vm.h
> > > @@ -303,6 +303,71 @@ void xe_vm_snapshot_capture_delayed(struct
> > > xe_vm_snapshot *snap);
> > > void xe_vm_snapshot_print(struct xe_vm_snapshot *snap, struct
> > > drm_printer *p);
> > > void xe_vm_snapshot_free(struct xe_vm_snapshot *snap);
> > >
> > > +/**
> > > + * xe_vm_set_validating() - Register this task as currently making
> > > bos resident
> > > + * @vm: Pointer to the vm or NULL.
> > > + *
> > > + * Register this task as currently making bos resident for the vm.
> > > Intended
> > > + * to avoid eviction by the same task of shared bos bound to the
> > > vm.
> > > + * Call with the vm's resv lock held.
> > > + *
> > > + * Return: A pin cookie that should be used for
> > > xe_vm_clear_validating().
> > > + */
> > > +static inline struct pin_cookie xe_vm_set_validating(struct xe_vm
> > > *vm,
> > > + bool
> > > allow_res_evict)
> > > +{
> > > + struct pin_cookie cookie = {};
> > > +
> > > + if (vm && !allow_res_evict) {
> > > + xe_vm_assert_held(vm);
> > > + cookie = lockdep_pin_lock(&xe_vm_resv(vm)-
> > > >lock.base);
> >
> > I'm little unclear on why the cookie is needed / what
> > lockdep_pin_lock
> > does. I looked implementation for lockdep_pin_lock and it completely
> > undocumented - could you explain?
>
> lockdep_pin_lock() warns if someone somewhere deeper in the call chain
> for some reason unlocks the specific lock while the lock is pinned.
>
Thanks. I was able to figure this out after a bit more digging too.
> In this case that would mean that vm->validating would be set without
> the vm->resv was held.
>
> Mostly paranoia.
Paranoia is good IMO.
With that:
Reviewed-by: Matthew Brost <matthew.brost at intel.com>
>
> /Thomas
>
> >
> > Everything else makes sense and LGTM.
> >
> > Matt
> >
> > > + /* Pairs with READ_ONCE in xe_vm_is_validating()
> > > */
> > > + WRITE_ONCE(vm->validating, current);
> > > + }
> > > +
> > > + return cookie;
> > > +}
> > > +
> > > +/**
> > > + * xe_vm_clear_validating() - Unregister this task as currently
> > > making bos resident
> > > + * @vm: Pointer to the vm or NULL
> > > + * @cookie: Cookie obtained from xe_vm_set_validating().
> > > + *
> > > + * Register this task as currently making bos resident for the vm.
> > > Intended
> > > + * to avoid eviction by the same task of shared bos bound to the
> > > vm.
> > > + * Call with the vm's resv lock held.
> > > + */
> > > +static inline void xe_vm_clear_validating(struct xe_vm *vm, bool
> > > allow_res_evict,
> > > + struct pin_cookie
> > > cookie)
> > > +{
> > > + if (vm && !allow_res_evict) {
> > > + lockdep_unpin_lock(&xe_vm_resv(vm)->lock.base,
> > > cookie);
> > > + /* Pairs with READ_ONCE in xe_vm_is_validating()
> > > */
> > > + WRITE_ONCE(vm->validating, NULL);
> > > + }
> > > +}
> > > +
> > > +/**
> > > + * xe_vm_is_validating() - Whether bos bound to the vm are
> > > currently being made resident
> > > + * by the current task.
> > > + * @vm: Pointer to the vm.
> > > + *
> > > + * If this function returns %true, we should be in a vm resv
> > > locked region, since
> > > + * the current process is the same task that called
> > > xe_vm_set_validating().
> > > + * The function asserts that that's indeed the case.
> > > + *
> > > + * Return: %true if the task is currently making bos resident,
> > > %false otherwise.
> > > + */
> > > +static inline bool xe_vm_is_validating(struct xe_vm *vm)
> > > +{
> > > + /* Pairs with WRITE_ONCE in xe_vm_is_validating() */
> > > + if (READ_ONCE(vm->validating) == current) {
> > > + xe_vm_assert_held(vm);
> > > + return true;
> > > + }
> > > + return false;
> > > +}
> > > +
> > > #if IS_ENABLED(CONFIG_DRM_XE_USERPTR_INVAL_INJECT)
> > > void xe_vma_userptr_force_invalidate(struct xe_userptr_vma *uvma);
> > > #else
> > > diff --git a/drivers/gpu/drm/xe/xe_vm_types.h
> > > b/drivers/gpu/drm/xe/xe_vm_types.h
> > > index bfc145baad49..0e1318a15c9e 100644
> > > --- a/drivers/gpu/drm/xe/xe_vm_types.h
> > > +++ b/drivers/gpu/drm/xe/xe_vm_types.h
> > > @@ -310,6 +310,14 @@ struct xe_vm {
> > > * protected by the vm resv.
> > > */
> > > u64 tlb_flush_seqno;
> > > + /**
> > > + * @validating: The task that is currently making bos
> > > resident for this vm.
> > > + * Protected by the VM's resv for writing. Opportunistic
> > > reading can be done
> > > + * using READ_ONCE. Note: This is a workaround for the
> > > + * TTM eviction_valuable() callback not being passed a
> > > struct
> > > + * ttm_operation_context(). Future work might want to
> > > address this.
> > > + */
> > > + struct task_struct *validating;
> > > /** @batch_invalidate_tlb: Always invalidate TLB before
> > > batch start */
> > > bool batch_invalidate_tlb;
> > > /** @xef: XE file handle for tracking this VM's drm client
> > > */
> > > --
> > > 2.49.0
> > >
>
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