linux-kernel - Re: [PATCH v1 1/1] fs/splice: add missing callback for inaccessible pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <540f483f-5e58-f342-e771-9d90c4d3fb6a@intel.com>
Date:   Thu, 30 Apr 2020 12:32:31 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        akpm@...ux-foundation.org, jack@...e.cz, kirill@...temov.name
Cc:     david@...hat.com, aarcange@...hat.com, linux-mm@...ck.org,
        frankja@...ux.ibm.com, sfr@...b.auug.org.au, jhubbard@...dia.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        peterz@...radead.org, sean.j.christopherson@...el.com
Subject: Re: [PATCH v1 1/1] fs/splice: add missing callback for inaccessible
 pages

On 4/30/20 11:12 AM, 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.

Ahh, nice catch!  That does explain an oddity or two that I saw.

> 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).

Yes, I see the same thing.

I updated the patch and double-checked that it triggers properly with a
socket-based sendfile().