[PATCH v3 19/19] drm/xe/bo: Update atomic_access attribute on madvise
Matthew Brost
matthew.brost at intel.com
Wed May 28 23:46:45 UTC 2025
On Tue, May 27, 2025 at 10:10:03PM +0530, Himal Prasad Ghimiray wrote:
> Update the bo_atomic_access based on user-provided input and determine
> the migration to smem during a CPU fault
>
> v2 (Matthew Brost)
> - Avoid cpu unmapping if bo is already in smem
> - check atomics on smem too for ioctl
> - Add comments
>
> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray at intel.com>
> ---
> drivers/gpu/drm/xe/xe_bo.c | 21 ++++++++++++--
> drivers/gpu/drm/xe/xe_vm.c | 11 ++++++--
> drivers/gpu/drm/xe/xe_vm_madvise.c | 45 ++++++++++++++++++++++++++++--
> 3 files changed, 69 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index d99d91fe8aa9..9072e8ae3f3e 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1662,6 +1662,12 @@ static void xe_gem_object_close(struct drm_gem_object *obj,
> }
> }
>
> +static bool should_migrate_to_smem(struct xe_bo *bo)
> +{
xe_bo_assert_held, more on that in reply to previous patch.
> + return bo->attr.atomic_access == DRM_XE_VMA_ATOMIC_GLOBAL ||
> + bo->attr.atomic_access == DRM_XE_VMA_ATOMIC_CPU;
> +}
> +
Hmm, this is tricky. I guess this means sharded atomics on BOs do not
just work whereas for SVM they do (i.e., DRM_XE_VMA_ATOMIC_UNDEFINED
means atomics do not work for BOs but for SVM they do). I suppose this
is the current behavior. I think this will need to be document in the
uAPI kernel doc.
> static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
> {
> struct ttm_buffer_object *tbo = vmf->vma->vm_private_data;
> @@ -1670,7 +1676,7 @@ static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
> struct xe_bo *bo = ttm_to_xe_bo(tbo);
> bool needs_rpm = bo->flags & XE_BO_FLAG_VRAM_MASK;
> vm_fault_t ret;
> - int idx;
> + int idx, r = 0;
>
> if (needs_rpm)
> xe_pm_runtime_get(xe);
> @@ -1682,8 +1688,17 @@ static vm_fault_t xe_gem_fault(struct vm_fault *vmf)
> if (drm_dev_enter(ddev, &idx)) {
> trace_xe_bo_cpu_fault(bo);
>
> - ret = ttm_bo_vm_fault_reserved(vmf, vmf->vma->vm_page_prot,
> - TTM_BO_VM_NUM_PREFAULT);
> + if (should_migrate_to_smem(bo)) {
> + r = xe_bo_migrate(bo, XE_PL_TT);
> + if (r == -EBUSY || r == -ERESTARTSYS || r == -EINTR)
> + ret = VM_FAULT_NOPAGE;
> + else if (r)
> + ret = VM_FAULT_SIGBUS;
> + }
> + if (!ret)
> + ret = ttm_bo_vm_fault_reserved(vmf,
> + vmf->vma->vm_page_prot,
> + TTM_BO_VM_NUM_PREFAULT);
> drm_dev_exit(idx);
> } else {
> ret = ttm_bo_vm_dummy_page(vmf, vmf->vma->vm_page_prot);
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 9611d7ca2bed..1bdf85c12374 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3116,9 +3116,16 @@ static int op_lock_and_prep(struct drm_exec *exec, struct xe_vm *vm,
> err = vma_lock_and_validate(exec,
> gpuva_to_vma(op->base.prefetch.va),
> false);
> - if (!err && !xe_vma_has_no_bo(vma))
> - err = xe_bo_migrate(xe_vma_bo(vma),
> + if (!err && !xe_vma_has_no_bo(vma)) {
> + struct xe_bo *bo = xe_vma_bo(vma);
> +
> + if (region == 0 && !vm->xe->info.has_device_atomics_on_smem &&
> + bo->attr.atomic_access == DRM_XE_VMA_ATOMIC_DEVICE)
> + region = 1;
I wonder if it better to just leave region as is and let the next atomic
fault trigger the migration.
> +
> + err = xe_bo_migrate(bo,
> region_to_mem_type[region]);
> + }
> break;
> }
> default:
> diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c
> index 0f0b94cb43f2..e048eb48826c 100644
> --- a/drivers/gpu/drm/xe/xe_vm_madvise.c
> +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c
> @@ -82,15 +82,54 @@ static int madvise_atomic(struct xe_device *xe, struct xe_vm *vm,
> struct xe_vma **vmas, int num_vmas,
> struct drm_xe_madvise_ops ops)
> {
> - int i;
> + struct xe_bo *bo;
> + int err, i;
>
> xe_assert(vm->xe, ops.type == DRM_XE_VMA_ATTR_ATOMIC);
> xe_assert(vm->xe, ops.atomic.val > DRM_XE_VMA_ATOMIC_UNDEFINED &&
> ops.atomic.val <= DRM_XE_VMA_ATOMIC_CPU);
>
Do you sanitize ops.atomic.val prior to this? Also do we disallow a user
setting DRM_XE_VMA_ATOMIC_UNDEFINED? If not, then this needs to be >=
DRM_XE_VMA_ATOMIC_UNDEFINED.
> - for (i = 0; i < num_vmas; i++)
> + for (i = 0; i < num_vmas; i++) {
> vmas[i]->attr.atomic_access = ops.atomic.val;
> - /*TODO: handle bo backed vmas */
> +
> + bo = xe_vma_bo(vmas[i]);
> + if (!bo)
> + continue;
> +
> + if (XE_IOCTL_DBG(xe, ops.atomic.val == DRM_XE_VMA_ATOMIC_CPU &&
> + !(bo->flags & XE_BO_FLAG_SYSTEM)))
> + return -EINVAL;
> +
Note when we fail here (or anywhere else in madvise), we could be in a
state where madvise has partially completed. I think that is actually ok
as nothing in madvise is fatal as we are just changing attributes. But I
think we need to document this in the uAPI kernel doc that if madvise
fails, the state of madvise attributes are undefined.
In practice this really should never fail unless a user is giving bad
input or extreme memory pressure and kmalloc fails.
Matt
> + /* NOTE: The following atomic checks are platform-specific. For example,
> + * if a device supports CXL atomics, these may not be necessary or
> + * may behave differently.
> + */
> + if (XE_IOCTL_DBG(xe, ops.atomic.val == DRM_XE_VMA_ATOMIC_DEVICE &&
> + !(bo->flags & XE_BO_FLAG_VRAM0) &&
> + !(bo->flags & XE_BO_FLAG_VRAM1) &&
> + !(bo->flags & XE_BO_FLAG_SYSTEM &&
> + xe->info.has_device_atomics_on_smem)))
> + return -EINVAL;
> +
> + if (XE_IOCTL_DBG(xe, ops.atomic.val == DRM_XE_VMA_ATOMIC_GLOBAL &&
> + (!(bo->flags & XE_BO_FLAG_SYSTEM) ||
> + (!(bo->flags & XE_BO_FLAG_VRAM0) &&
> + !(bo->flags & XE_BO_FLAG_VRAM1)))))
> + return -EINVAL;
> +
> + err = xe_bo_lock(bo, true);
> + if (err)
> + return err;
> + bo->attr.atomic_access = ops.atomic.val;
> +
> + /* Invalidate cpu page table, so bo can migrate to smem in next access */
> + if (xe_bo_is_vram(bo) &&
> + (bo->attr.atomic_access == DRM_XE_VMA_ATOMIC_CPU ||
> + bo->attr.atomic_access == DRM_XE_VMA_ATOMIC_GLOBAL))
> + ttm_bo_unmap_virtual(&bo->ttm);
> +
> + xe_bo_unlock(bo);
> + }
> return 0;
> }
>
> --
> 2.34.1
>
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