linux-kernel - Re: [PATCH] mm/memcg: fix device private memcg accounting

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 for Android: free password hash cracker in your pocket

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

Date:   Fri, 9 Oct 2020 17:00:37 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Michal Hocko" <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Balbir Singh <bsingharora@...il.com>,
        Ira Weiny <ira.weiny@...el.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH] mm/memcg: fix device private memcg accounting


On 10/9/20 3:50 PM, Andrew Morton wrote:
> On Fri, 9 Oct 2020 14:59:52 -0700 Ralph Campbell <rcampbell@...dia.com> wrote:
> 
>> The code in mc_handle_swap_pte() checks for non_swap_entry() and returns
>> NULL before checking is_device_private_entry() so device private pages
>> are never handled.
>> Fix this by checking for non_swap_entry() after handling device private
>> swap PTEs.
>>
>> Cc: stable@...r.kernel.org
> 
> I was going to ask "what are the end-user visible effects of the bug".
> This is important information with a cc:stable.
> 
>>
>> I'm not sure exactly how to test this. I ran the HMM self tests but
>> that is a minimal sanity check. I think moving the self test from one
>> memory cgroup to another while it is running would exercise this patch.
>> I'm looking at how the test could move itself to another group after
>> migrating some anonymous memory to the test driver.
>>
> 
> But this makes me suspect the answer is "there aren't any that we know
> of".  Are you sure a cc:stable is warranted?
> 

I assume the memory cgroup accounting would be off somehow when moving
a process to another memory cgroup.
Currently, the device private page is charged like a normal anonymous page
when allocated and is uncharged when the page is freed so I think that path is OK.
Maybe someone who knows more about memory cgroup accounting can comment?