Re: [Intel-xe] [PATCH 3/4] drm/xe/vm: Perform accounting of userptr pinned pages

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Aug 18, 2023 at 05:08:44PM +0200, Thomas Hellström wrote:
> Account these pages against RLIMIT_MEMLOCK following how RDMA does this
> with CAP_IPC_LOCK bypassing the limit.
> 
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Patch LGTM but nits on naming + possible assert.

> ---
>  drivers/gpu/drm/xe/xe_vm.c | 43 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index ecbcad696b60..d9c000689002 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -34,6 +34,33 @@
>  
>  #define TEST_VM_ASYNC_OPS_ERROR
>  
> +/*
> + * Perform userptr PIN accounting against RLIMIT_MEMLOCK for now, similarly
> + * to how RDMA does this.
> + */
> +static int xe_vma_mlock_alloc(struct xe_vma *vma, unsigned long num_pages)
> +{

xe_vma_userptr_mlock_alloc? or maybe even xe_vma_userptr_mlock_reserve?

> +	unsigned long lock_limit, new_pinned;
> +	struct mm_struct *mm = vma->userptr.notifier.mm;
> +

This be a candidate to use the new aseert macros to ensure that the vma
is a userptr + pinned? Not sure if that merged yet.

> +	if (!can_do_mlock())
> +		return -EPERM;
> +
> +	lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> +	new_pinned = atomic64_add_return(num_pages, &mm->pinned_vm);
> +	if (new_pinned > lock_limit && !capable(CAP_IPC_LOCK)) {
> +		atomic64_sub(num_pages, &mm->pinned_vm);
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +static void xe_vma_mlock_free(struct xe_vma *vma, unsigned long num_pages)
> +{

xe_vma_userptr_mlock_free? or maybe even xe_vma_userptr_mlock_release?

Same for the assert here.

Anyways, I'll leave addressing these nits up to you, with that:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> +	atomic64_sub(num_pages, &vma->userptr.notifier.mm->pinned_vm);
> +}
> +
>  /**
>   * xe_vma_userptr_check_repin() - Advisory check for repin needed
>   * @vma: The userptr vma
> @@ -89,9 +116,17 @@ int xe_vma_userptr_pin_pages(struct xe_vma *vma)
>  					    !read_only);
>  		pages = vma->userptr.pinned_pages;
>  	} else {
> +		if (xe_vma_is_pinned(vma)) {
> +			ret = xe_vma_mlock_alloc(vma, num_pages);
> +			if (ret)
> +				return ret;
> +		}
> +
>  		pages = kvmalloc_array(num_pages, sizeof(*pages), GFP_KERNEL);
> -		if (!pages)
> -			return -ENOMEM;
> +		if (!pages) {
> +			ret = -ENOMEM;
> +			goto out_account;
> +		}
>  	}
>  
>  	pinned = ret = 0;
> @@ -187,6 +222,9 @@ int xe_vma_userptr_pin_pages(struct xe_vma *vma)
>  mm_closed:
>  	kvfree(pages);
>  	vma->userptr.pinned_pages = NULL;
> +out_account:
> +	if (xe_vma_is_pinned(vma))
> +		xe_vma_mlock_free(vma, num_pages);
>  	return ret;
>  }
>  
> @@ -1004,6 +1042,7 @@ static void xe_vma_destroy_late(struct xe_vma *vma)
>  			unpin_user_pages_dirty_lock(vma->userptr.pinned_pages,
>  						    vma->userptr.num_pinned,
>  						    !read_only);
> +			xe_vma_mlock_free(vma, xe_vma_size(vma) >> PAGE_SHIFT);
>  			kvfree(vma->userptr.pinned_pages);
>  		}
>  
> -- 
> 2.41.0
>