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Thu, 30 Apr 2020 20:04:48 +0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 03UK4jCu1704426 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 Apr 2020 20:04:45 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2601EAE04D; Thu, 30 Apr 2020 20:04:45 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 24C87AE051; Thu, 30 Apr 2020 20:04:44 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.16.167]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 30 Apr 2020 20:04:44 +0000 (GMT) Subject: Re: [PATCH v2 1/1] fs/splice: add missing callback for inaccessible pages To: Claudio Imbrenda , viro@zeniv.linux.org.uk Cc: david@redhat.com, akpm@linux-foundation.org, aarcange@redhat.com, linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au, jhubbard@nvidia.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, jack@suse.cz, kirill@shutemov.name, dave.hansen@intel.com, peterz@infradead.org, sean.j.christopherson@intel.com, Ulrich.Weigand@de.ibm.com References: <20200430143825.3534128-1-imbrenda@linux.ibm.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200430143825.3534128-1-imbrenda@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-30_12:2020-04-30,2020-04-30 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 priorityscore=1501 mlxscore=0 clxscore=1015 impostorscore=0 phishscore=0 bulkscore=0 spamscore=0 lowpriorityscore=0 adultscore=0 mlxlogscore=999 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004300147 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.04.20 16:38, Claudio Imbrenda wrote: > Inaccessible pages are pages that should not be accessed by any device, > and belong to a protected VM. If any such pages are passed to a > device, there will be I/O errors, which will not always be recoverable, > depending on the architecture and on the specific device. > > CPU accesses to inaccessible pages are less problematic, since they are > always recoverable. > > Page cache and direct I/O were fixed in a previous patch, in which a > architecture hook is provided to make the page accessible by I/O > devices. > > One possible remaining path to sneak a protected page directly to a > device is sendfile and similar syscalls. Those syscalls take a page > directly from the page cache and give them directly to the device with > zero-copy. This bypasses both existing hooks in gup and in writeback. > > This patch fixes the issue by adding a call to arch_make_page_accessible > in page_cache_pipe_buf_confirm, thus fixing the issue. > > Notice that we only need to make sure the source is accessible, since > zero-copy only works in one direction, and CPU accesses to inaccessible > pages are not a problem. Pagecache-to-pagecache is also not a problem > since that is done by the CPU. > > The hook has no overhead for architectures that do not need to deal > with inaccessible pages. > > Fixes: f28d43636d6f ("mm/gup/writeback: add callbacks for inaccessible pages") You should add a Reported-by Dave Hansen, I guess. Acked-by: Christian Borntraeger > Signed-off-by: Claudio Imbrenda > --- > fs/splice.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/fs/splice.c b/fs/splice.c > index 4735defc46ee..f026e0ce9acd 100644 > --- a/fs/splice.c > +++ b/fs/splice.c > @@ -106,6 +106,9 @@ static int page_cache_pipe_buf_confirm(struct pipe_inode_info *pipe, > struct page *page = buf->page; > int err; > > + if (arch_make_page_accessible(page)) > + return -EIO; > + > if (!PageUptodate(page)) { > lock_page(page); > >