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Thu, 30 Apr 2020 19:54:15 +0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 03UJsC9k4915488 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 Apr 2020 19:54:12 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B0404AE045; Thu, 30 Apr 2020 19:54:12 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CDBCAAE053; Thu, 30 Apr 2020 19:54:11 +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 19:54:11 +0000 (GMT) Subject: Re: [PATCH v1 1/1] fs/splice: add missing callback for inaccessible pages From: Christian Borntraeger To: Dave Hansen , Claudio Imbrenda , akpm@linux-foundation.org, jack@suse.cz, kirill@shutemov.name, John Hubbard Cc: david@redhat.com, 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, peterz@infradead.org, sean.j.christopherson@intel.com References: <20200428225043.3091359-1-imbrenda@linux.ibm.com> <2a1abf38-d321-e3c7-c3b1-53b6db6da310@intel.com> <4b32c162-6ea4-ba91-b6d5-8961b7dff6e8@de.ibm.com> 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: <4b32c162-6ea4-ba91-b6d5-8961b7dff6e8@de.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 mlxlogscore=999 adultscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 lowpriorityscore=0 phishscore=0 spamscore=0 clxscore=1015 bulkscore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004300145 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30.04.20 21:02, Christian Borntraeger wrote: > On 30.04.20 20:12, Christian Borntraeger wrote: >> >> >> On 29.04.20 18:07, Dave Hansen wrote: >>> On 4/28/20 3:50 PM, Claudio Imbrenda wrote: >>>> If a page is inaccesible and it is used for things like sendfile, then >>>> the content of the page is not always touched, and can be passed >>>> directly to a driver, causing issues. >>>> >>>> This patch fixes the issue by adding a call to arch_make_page_accessible >>>> in page_cache_pipe_buf_confirm; this fixes the issue. >>> >>> I spent about 5 minutes putting together a patch: >>> >>> https://sr71.net/~dave/intel/accessible.patch >> >> You only set the page flag for compound pages. that of course leaves a big pile >> of pages marked a not accessible, thus explaining the sendto trace and all kind >> of other random traces. >> >> >> What do you see when you also do the SetPageAccessible(page); >> in the else page of prep_new_page (order == 0). >> (I do get > 10000 of these non compound page allocs just during boot). >> > > And yes, I think you are right that we should call the callback also for !FOLL_PIN. Thinking again about this I am no longer sure. Adding John Hubbard. Documentation/core-api/pin_user_pages.rst says: -------snip---------- Another way of thinking about these flags is as a progression of restrictions: FOLL_GET is for struct page manipulation, without affecting the data that the struct page refers to. FOLL_PIN is a *replacement* for FOLL_GET, and is for short term pins on pages whose data *will* get accessed. As such, FOLL_PIN is a "more severe" form of pinning. And finally, FOLL_LONGTERM is an even more restrictive case that has FOLL_PIN as a prerequisite: this is for pages that will be pinned longterm, and whose data will be accessed. -------snip---------- So John,is it ok to give a page to an I/O device where the code has used gup with FOLL_GET (or gup fast without pup) or would you consider this a bug?