linux-kernel - Re: [PATCH 1/3] drivers/gpu/drm/via: convert put_page() to put_user

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Date:   Mon, 22 Jul 2019 11:33:55 +0200
From:   Christoph Hellwig <hch@....de>
To:     john.hubbard@...il.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Björn Töpel <bjorn.topel@...el.com>,
        Boaz Harrosh <boaz@...xistor.com>,
        Christoph Hellwig <hch@....de>,
        Daniel Vetter <daniel@...ll.ch>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ilya Dryomov <idryomov@...il.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jérôme Glisse <jglisse@...hat.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ming Lei <ming.lei@...hat.com>, Sage Weil <sage@...hat.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        Yan Zheng <zyan@...hat.com>, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
        linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 1/3] drivers/gpu/drm/via: convert put_page() to
 put_user_page*()

On Sun, Jul 21, 2019 at 09:30:10PM -0700, john.hubbard@...il.com wrote:
>  		for (i = 0; i < vsg->num_pages; ++i) {
>  			if (NULL != (page = vsg->pages[i])) {
>  				if (!PageReserved(page) && (DMA_FROM_DEVICE == vsg->direction))
> -					SetPageDirty(page);
> -				put_page(page);
> +					put_user_pages_dirty(&page, 1);
> +				else
> +					put_user_page(page);
>  			}

Can't just pass a dirty argument to put_user_pages?  Also do we really
need a separate put_user_page for the single page case?
put_user_pages_dirty?

Also the PageReserved check looks bogus, as I can't see how a reserved
page can end up here.  So IMHO the above snippled should really look
something like this:

	put_user_pages(vsg->pages[i], vsg->num_pages,
			vsg->direction == DMA_FROM_DEVICE);

in the end.