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

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Message-ID: <397ff3e4-e857-037a-1aee-ff6242e024b2@nvidia.com>
Date:   Mon, 22 Jul 2019 11:53:54 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@....de>, <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>,
        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>
Subject: Re: [PATCH 1/3] drivers/gpu/drm/via: convert put_page() to
 put_user_page*()

On 7/22/19 2:33 AM, Christoph Hellwig wrote:
> 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

Yes, and in fact that would help a lot more than the single page case,
which is really just cosmetic after all.

> need a separate put_user_page for the single page case?
> put_user_pages_dirty?

Not really. I'm still zeroing in on the ideal API for all these call sites,
and I agree that the approach below is cleaner.

> 
> 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.
> 

Agreed.

thanks,
-- 
John Hubbard
NVIDIA