[PATCH 15/21] drm/xe/eudebug: implement userptr_vma access

[Matthew Brost]

On Fri, Jul 26, 2024 at 05:08:12PM +0300, Mika Kuoppala wrote:
> From: Andrzej Hajda <andrzej.hajda at intel.com>
> 
> Debugger needs to read/write program's vmas including userptr_vma.
> Since hmm_range_fault is used to pin userptr vmas, it is possible
> to map those vmas from debugger context.
> 
> v2: kmap to kmap_local (Maciej)
> 
> Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>
> Signed-off-by: Maciej Patelczyk <maciej.patelczyk at intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_eudebug.c | 56 ++++++++++++++++++++++++++++++++-
>  1 file changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_eudebug.c b/drivers/gpu/drm/xe/xe_eudebug.c
> index aa383accc468..947331c19f43 100644
> --- a/drivers/gpu/drm/xe/xe_eudebug.c
> +++ b/drivers/gpu/drm/xe/xe_eudebug.c
> @@ -33,6 +33,7 @@
>  #include "xe_mmio.h"
>  #include "xe_module.h"
>  #include "xe_pm.h"
> +#include "xe_res_cursor.h"
>  #include "xe_rtp.h"
>  #include "xe_sched_job.h"
>  #include "xe_vm.h"
> @@ -2852,6 +2853,58 @@ static void discovery_work_fn(struct work_struct *work)
>  	xe_eudebug_put(d);
>  }
>  
> +static int xe_eudebug_uvma_access(struct xe_userptr_vma *uvma, u64 offset,
> +				  void *buf, u64 len, bool write)
> +{
> +	struct xe_vm *vm = xe_vma_vm(&uvma->vma);
> +	struct xe_userptr *up = &uvma->userptr;
> +	struct xe_res_cursor cur = {};
> +	int cur_len, ret = 0;
> +
> +	/* lock notifier in non-invalidation state */
> +	for (unsigned long nseq = uvma->userptr.notifier_seq; true;
> +	     nseq = mmu_interval_read_begin(&uvma->userptr.notifier)) {
> +		down_read(&vm->userptr.notifier_lock);
> +		if (!mmu_interval_read_retry(&uvma->userptr.notifier, nseq))
> +			break;
> +		up_read(&vm->userptr.notifier_lock);
> +	}
> +

I don't think this will work without lockdep blowing up.
'&vm->userptr.notifier_lock' is taken in the MMU notifier, the MMU
notifier is in the path of reclaim, thus you cannot allocate memory
under this lock, xe_vma_userptr_pin_pages allocates memory.

I think you are going to need to pin the pages first, then take the
notifier_lock, recheck the seqno, retry on a miscomapre, once the
compare passes it should be safe to write the userptr.

Matt

> +	/* re-pin if necessary */
> +	if (xe_vma_userptr_check_repin(uvma)) {
> +		spin_lock(&vm->userptr.invalidated_lock);
> +		list_del_init(&uvma->userptr.invalidate_link);
> +		spin_unlock(&vm->userptr.invalidated_lock);
> +
> +		ret = xe_vma_userptr_pin_pages(uvma);
> +		if (ret)
> +			goto out_unlock_notifier;
> +	}
> +
> +	if (!up->sg) {
> +		ret = -EINVAL;
> +		goto out_unlock_notifier;
> +	}
> +
> +	for (xe_res_first_sg(up->sg, offset, len, &cur); cur.remaining;
> +	     xe_res_next(&cur, cur_len)) {
> +		void *ptr = kmap_local_page(sg_page(cur.sgl)) + cur.start;
> +
> +		cur_len = min(cur.size, cur.remaining);
> +		if (write)
> +			memcpy(ptr, buf, cur_len);
> +		else
> +			memcpy(buf, ptr, cur_len);
> +		kunmap_local(ptr);
> +		buf += cur_len;
> +	}
> +	ret = len;
> +
> +out_unlock_notifier:
> +	up_read(&vm->userptr.notifier_lock);
> +	return ret;
> +}
> +
>  static int xe_eudebug_bovma_access(struct xe_bo *bo, u64 offset,
>  				   void *buf, u64 len, bool write)
>  {
> @@ -2895,7 +2948,8 @@ static int xe_eudebug_vma_access(struct xe_vma *vma, u64 offset,
>  	if (bo)
>  		return xe_eudebug_bovma_access(bo, offset, buf, bytes, write);
>  
> -	return -EOPNOTSUPP;
> +	return xe_eudebug_uvma_access(to_userptr_vma(vma), offset,
> +				      buf, bytes, write);
>  }
>  
>  static int xe_eudebug_vm_access(struct xe_vm *vm, u64 offset,
> -- 
> 2.34.1
>