netdev - Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL

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Message-ID: <290ba4aa-247e-6570-9eff-ccf2087e1120@nvidia.com>
Date:   Wed, 13 Nov 2019 12:19:50 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Ira Weiny <ira.weiny@...el.com>, Jason Gunthorpe <jgg@...pe.ca>
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>,
        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>,
        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 v4 08/23] vfio, mm: fix get_user_pages_remote() and
 FOLL_LONGTERM

On 11/13/19 11:17 AM, Ira Weiny wrote:
...
>>> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>>>   		flags |= FOLL_WRITE;
>>>   
>>>   	down_read(&mm->mmap_sem);
>>> -	if (mm == current->mm) {
>>> -		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
>>> -				     vmas);
>>> -	} else {
>>> -		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
>>> -					    vmas, NULL);
>>> -		/*
>>> -		 * The lifetime of a vaddr_get_pfn() page pin is
>>> -		 * userspace-controlled. In the fs-dax case this could
>>> -		 * lead to indefinite stalls in filesystem operations.
>>> -		 * Disallow attempts to pin fs-dax pages via this
>>> -		 * interface.
>>> -		 */
>>> -		if (ret > 0 && vma_is_fsdax(vmas[0])) {
>>> -			ret = -EOPNOTSUPP;
>>> -			put_page(page[0]);
>>> -		}
>>> -	}
>>> -	up_read(&mm->mmap_sem);
>>> -
>>> +	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
>>> +				    page, NULL, NULL);
>>>   	if (ret == 1) {
>>>   		*pfn = page_to_pfn(page[0]);
>>>   		return 0;
>>
>> Mind the return with the lock held this needs some goto unwind
> 
> Ah yea...  retract my reviewed by...  :-(
> 

ooops, embarrassed that I missed that, good catch. Will repost with it fixed.



thanks,
-- 
John Hubbard
NVIDIA