[Intel-xe] [PATCH v4] drm/xe: Extend scratch page support to fault mode

[Matthew Brost]

On Tue, Nov 14, 2023 at 04:56:11PM -0800, Brian Welty wrote:
> The PVC HW has a limitation that the page fault due to invalid access
> will halt the corresponding EUs. So, in order to activate the debugger,
> kmd needs to setup the scratch pages to unhalt the EUs.
> 
> This feature can only be enabled if scratch flag is set per VM during
> VM_CREATE. For use with EU debugger, the debugger umd will set the flag.
> 
> The idea is to bind a scratch vma if the page fault is from an invalid
> access. This patch is taking advantage of null pte. After the bind, the
> user application can continue to run without causing a GPU hang or reset.
> 
> In case the app will bind this scratch vma to a valid address, GPUVA
> handles all of this (e.g. it will create ops to unbind the old VMA and
> bind the new one).
> Future optimization: as we use null pte, it may not require to invalidate
> TLBs when doing unbind if all upper layer page tables are unmodified.
> 
> v2: per Matt's suggestion, remove the scratch page unbind.
> v3: correct error handlings.
> v4: add test for XE_VM_FLAG_64K, and ALIGN_DOWN the address
> 
> Signed-off-by: Bruce Chang <yu.bruce.chang at intel.com>
> Reviewed-by: Brian Welty <brian.welty at intel.com>
> Acked-by: Stuart Summers <stuart.summers at intel.com>
> Signed-off-by: Brian Welty <brian.welty at intel.com>

Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> ---
>  drivers/gpu/drm/xe/xe_gt_pagefault.c |  9 ++++--
>  drivers/gpu/drm/xe/xe_vm.c           | 42 ++++++++++++++++++++++++----
>  drivers/gpu/drm/xe/xe_vm.h           |  2 ++
>  3 files changed, 46 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> index 5b3585e2c125..91ad843713a6 100644
> --- a/drivers/gpu/drm/xe/xe_gt_pagefault.c
> +++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c
> @@ -161,8 +161,13 @@ static int handle_pagefault(struct xe_gt *gt, struct pagefault *pf)
>  	write_locked = true;
>  	vma = lookup_vma(vm, pf->page_addr);
>  	if (!vma) {
> -		ret = -EINVAL;
> -		goto unlock_vm;
> +		if (vm->flags & XE_VM_FLAG_SCRATCH_PAGE)
> +			vma = xe_vm_create_scratch_vma(vm, pf->page_addr);
> +
> +		if (IS_ERR_OR_NULL(vma)) {
> +			ret = -EINVAL;
> +			goto unlock_vm;
> +		}
>  	}
>  
>  	if (!xe_vma_is_userptr(vma) || !xe_vma_userptr_check_repin(vma)) {
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index d45f4f1d490f..191a1d2e9835 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -1397,7 +1397,13 @@ struct xe_vm *xe_vm_create(struct xe_device *xe, u32 flags)
>  		}
>  	}
>  
> -	if (flags & XE_VM_FLAG_SCRATCH_PAGE) {
> +	if (flags & XE_VM_FLAG_SCRATCH_PAGE &&
> +	    !(flags & XE_VM_FLAG_FAULT_MODE)) {
> +		/*
> +		 * Create a global scratch page for mapping the whole VM's
> +		 * address space. However, in fault mode, we instead defer
> +		 * creation of scratch (null pte) to the fault handler.
> +		 */
>  		for_each_tile(tile, xe, id) {
>  			if (!vm->pt_root[id])
>  				continue;
> @@ -1951,10 +1957,6 @@ int xe_vm_create_ioctl(struct drm_device *dev, void *data,
>  	if (XE_IOCTL_DBG(xe, args->flags & ~ALL_DRM_XE_VM_CREATE_FLAGS))
>  		return -EINVAL;
>  
> -	if (XE_IOCTL_DBG(xe, args->flags & DRM_XE_VM_CREATE_SCRATCH_PAGE &&
> -			 args->flags & DRM_XE_VM_CREATE_FAULT_MODE))
> -		return -EINVAL;
> -
>  	if (XE_IOCTL_DBG(xe, args->flags & DRM_XE_VM_CREATE_COMPUTE_MODE &&
>  			 args->flags & DRM_XE_VM_CREATE_FAULT_MODE))
>  		return -EINVAL;
> @@ -3269,6 +3271,36 @@ int xe_vm_invalidate_vma(struct xe_vma *vma)
>  	return 0;
>  }
>  
> +struct xe_vma *xe_vm_create_scratch_vma(struct xe_vm *vm, u64 addr)
> +{
> +	struct xe_vma *vma;
> +	u64 end;
> +	int err;
> +
> +	if (xe_vm_is_closed_or_banned(vm))
> +		return ERR_PTR(-ENOENT);
> +
> +	if (vm->flags & XE_VM_FLAG_64K) {
> +		addr = ALIGN_DOWN(addr, SZ_64K);
> +		end = addr + SZ_64K - 1;
> +	} else {
> +		end = addr + PAGE_SIZE - 1;
> +	}
> +	vma = xe_vma_create(vm, NULL, 0, addr, end, false, true, 0);
> +	if (IS_ERR_OR_NULL(vma))
> +		return vma;
> +
> +	err = xe_vm_insert_vma(vm, vma);
> +	if (err) {
> +		xe_vma_destroy_late(vma);
> +		return ERR_PTR(err);
> +	}
> +
> +	/* fault will handle the bind */
> +
> +	return vma;
> +}
> +
>  int xe_analyze_vm(struct drm_printer *p, struct xe_vm *vm, int gt_id)
>  {
>  	struct drm_gpuva *gpuva;
> diff --git a/drivers/gpu/drm/xe/xe_vm.h b/drivers/gpu/drm/xe/xe_vm.h
> index b08c75fbd8a1..e07ced37223d 100644
> --- a/drivers/gpu/drm/xe/xe_vm.h
> +++ b/drivers/gpu/drm/xe/xe_vm.h
> @@ -180,6 +180,8 @@ struct dma_fence *xe_vm_rebind(struct xe_vm *vm, bool rebind_worker);
>  
>  int xe_vm_invalidate_vma(struct xe_vma *vma);
>  
> +struct xe_vma *xe_vm_create_scratch_vma(struct xe_vm *vm, u64 addr);
> +
>  extern struct ttm_device_funcs xe_ttm_funcs;
>  
>  struct ttm_buffer_object *xe_vm_ttm_bo(struct xe_vm *vm);
> -- 
> 2.38.0
>