linux-kernel - Re: [PATCH v2 09/18] drm/via: set FOLL_PIN via pin_user_pages

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Message-ID: <880dbf76-ba9d-2555-27e4-a656c7cd3296@nvidia.com>
Date:   Mon, 4 Nov 2019 10:22:23 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Jerome Glisse <jglisse@...hat.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, <bpf@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <kvm@...r.kernel.org>,
        <linux-block@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
        <linuxppc-dev@...ts.ozlabs.org>, <netdev@...r.kernel.org>,
        <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 09/18] drm/via: set FOLL_PIN via pin_user_pages_fast()

On 11/4/19 9:44 AM, Jerome Glisse wrote:
> On Sun, Nov 03, 2019 at 01:18:04PM -0800, John Hubbard wrote:
>> Convert drm/via to use the new pin_user_pages_fast() call, which sets
>> FOLL_PIN. Setting FOLL_PIN is now required for code that requires
>> tracking of pinned pages, and therefore for any code that calls
>> put_user_page().
>>
>> Reviewed-by: Ira Weiny <ira.weiny@...el.com>
>> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> 
> Please be more explicit that via_dmablit.c is already using put_user_page()
> as i am expecting that any conversion to pin_user_pages*() must be pair with
> a put_user_page(). I find above commit message bit unclear from that POV.
> 

OK. This one, and the fs/io_uring (patch 9) and net/xdp (patch 10) were all
cases that had put_user_page() pre-existing. I will add something like the 
following to each commit description, for v3:

In partial anticipation of this work, the drm/via driver was already 
calling put_user_page() instead of put_page(). Therefore, in order to
convert from the get_user_pages()/put_page() model, to the
pin_user_pages()/put_user_page() model, the only change required
is to change get_user_pages() to pin_user_pages().

thanks,

John Hubbard
NVIDIA

> Reviewed-by: Jérôme Glisse <jglisse@...hat.com>
> 
> 
>> ---
>>  drivers/gpu/drm/via/via_dmablit.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/via/via_dmablit.c b/drivers/gpu/drm/via/via_dmablit.c
>> index 3db000aacd26..37c5e572993a 100644
>> --- a/drivers/gpu/drm/via/via_dmablit.c
>> +++ b/drivers/gpu/drm/via/via_dmablit.c
>> @@ -239,7 +239,7 @@ via_lock_all_dma_pages(drm_via_sg_info_t *vsg,  drm_via_dmablit_t *xfer)
>>  	vsg->pages = vzalloc(array_size(sizeof(struct page *), vsg->num_pages));
>>  	if (NULL == vsg->pages)
>>  		return -ENOMEM;
>> -	ret = get_user_pages_fast((unsigned long)xfer->mem_addr,
>> +	ret = pin_user_pages_fast((unsigned long)xfer->mem_addr,
>>  			vsg->num_pages,
>>  			vsg->direction == DMA_FROM_DEVICE ? FOLL_WRITE : 0,
>>  			vsg->pages);
>> -- 
>> 2.23.0
>>
> 
>