linux-kernel - Re: [PATCH] drm/radeon: Convert get_user_pages() --> pin_user

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Message-ID: <69a033cf-63b2-7da6-6a5e-a5bbc94b8afb@nvidia.com>
Date:   Tue, 26 May 2020 15:57:45 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        <alexander.deucher@....com>, <christian.koenig@....com>,
        <David1.Zhou@....com>, <daniel@...ll.ch>
CC:     <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/radeon: Convert get_user_pages() --> pin_user_pages()

On 2020-05-26 14:00, Souptick Joarder wrote:
> This code was using get_user_pages(), in a "Case 2" scenario
> (DMA/RDMA), using the categorization from [1]. That means that it's
> time to convert the get_user_pages() + release_pages() calls to
> pin_user_pages() + unpin_user_pages() calls.
> 
> There is some helpful background in [2]: basically, this is a small
> part of fixing a long-standing disconnect between pinning pages, and
> file systems' use of those pages.
> 
> [1] Documentation/core-api/pin_user_pages.rst
> 
> [2] "Explicit pinning of user-space pages":
>      https://lwn.net/Articles/807108/
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> 
> Hi,
> 
> I'm compile tested this, but unable to run-time test, so any testing
> help is much appriciated.
> ---
>   drivers/gpu/drm/radeon/radeon_ttm.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
> index 5d50c9e..e927de2 100644
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -506,7 +506,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>   		uint64_t userptr = gtt->userptr + pinned * PAGE_SIZE;
>   		struct page **pages = ttm->pages + pinned;
>   
> -		r = get_user_pages(userptr, num_pages, write ? FOLL_WRITE : 0,
> +		r = pin_user_pages(userptr, num_pages, write ? FOLL_WRITE : 0,
>   				   pages, NULL);
>   		if (r < 0)
>   			goto release_pages;
> @@ -535,7 +535,7 @@ static int radeon_ttm_tt_pin_userptr(struct ttm_tt *ttm)
>   	kfree(ttm->sg);
>   
>   release_pages:
> -	release_pages(ttm->pages, pinned);
> +	unpin_user_pages(ttm->pages, pinned);
>   	return r;
>   }
>   
> @@ -562,7 +562,7 @@ static void radeon_ttm_tt_unpin_userptr(struct ttm_tt *ttm)
>   			set_page_dirty(page);


Maybe we also need a preceding patch, to fix the above? It should be
set_page_dirty_lock(), rather than set_page_dirty(), unless I'm overlooking
something (which is very possible!).

Either way, from a tunnel vision perspective of changing gup to pup, this
looks good to me, so

     Acked-by: John Hubbard <jhubbard@...dia.com>


thanks,
-- 
John Hubbard
NVIDIA

>   
>   		mark_page_accessed(page);
> -		put_page(page);
> +		unpin_user_page(page);
>   	}
>   
>   	sg_free_table(ttm->sg);
>