linux-kernel - Re: [PATCH 21/21] nvme: Support atomic writes

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: <61b25fe8-22ae-c299-3225-ca835b337d41@oracle.com>
Date:   Thu, 9 Nov 2023 19:08:40 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>
Cc:     axboe@...nel.dk, kbusch@...nel.org, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com, djwong@...nel.org,
        viro@...iv.linux.org.uk, brauner@...nel.org,
        chandan.babu@...cle.com, dchinner@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-api@...r.kernel.org, Alan Adamson <alan.adamson@...cle.com>
Subject: Re: [PATCH 21/21] nvme: Support atomic writes

On 09/11/2023 15:46, Christoph Hellwig wrote:
> On Thu, Nov 09, 2023 at 03:42:40PM +0000, Matthew Wilcox wrote:
>> That wasn't the model we had in mind.  In our thinking, it was fine to
>> send a write that crossed the atomic write limit, but the drive wouldn't
>> guarantee that it was atomic except at the atomic write boundary.
>> Eg with an AWUN of 16kB, you could send five 16kB writes, combine them
>> into a single 80kB write, and if the power failed midway through, the
>> drive would guarantee that it had written 0, 16kB, 32kB, 48kB, 64kB or
>> all 80kB.  Not necessarily in order; it might have written bytes 16-32kB,
>> 64-80kB and not the other three.

I didn't think that there are any atomic write guarantees at all if we 
ever exceed AWUN or AWUPF or cross the atomic write boundary (if any).

> I can see some use for that, but I'm really worried that debugging
> problems in the I/O merging and splitting will be absolute hell.

Even if bios were merged for NVMe the total request length still should 
not exceed AWUPF. However a check can be added to ensure this for a 
submitted atomic write request.

As for splitting, it is not permitted for atomic writes and only a 
single bio is permitted to be created per write. Are more integrity 
checks required?

Thanks,
John