linux-kernel - Re: [PATCH v4 23/23] mm/gup: remove support for gup(FOLL

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Message-ID: <4e24c5af-bd96-e7c7-179b-0ca0f6abb852@nvidia.com>
Date:   Wed, 13 Nov 2019 15:27:00 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.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>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
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Subject: Re: [PATCH v4 23/23] mm/gup: remove support for gup(FOLL_LONGTERM)

On 11/13/19 11:09 AM, Ira Weiny wrote:
...
>> diff --git a/mm/gup.c b/mm/gup.c
>> index 82e7e4ce5027..90f5f95ee7ac 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -1756,11 +1756,11 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>>   		struct vm_area_struct **vmas)
>>   {
>>   	/*
>> -	 * FOLL_PIN must only be set internally by the pin_user_page*() and
>> -	 * pin_longterm_*() APIs, never directly by the caller, so enforce that
>> -	 * with an assertion:
>> +	 * FOLL_PIN and FOLL_LONGTERM must only be set internally by the
>> +	 * pin_user_page*() and pin_longterm_*() APIs, never directly by the
>> +	 * caller, so enforce that with an assertion:
>>   	 */
>> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
>> +	if (WARN_ON_ONCE(gup_flags & (FOLL_PIN | FOLL_LONGTERM)))
> 
> Don't we want to block FOLL_LONGTERM in get_user_pages_fast() as well after all
> this?
> 

Yes. But with the latest idea to restore FOLL_LONGTERM to its original glory,
that won't be an issue in the next version. heh.


thanks,
-- 
John Hubbard
NVIDIA