linux-kernel - Re: [PATCH RFC v3 00/11] scsi: ufs: Remove overzealous memory barriers

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]

Date: Thu, 21 Dec 2023 20:13:17 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Andrew Halaney <ahalaney@...hat.com>, Andy Gross <agross@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>,
 Manivannan Sadhasivam <mani@...nel.org>,
 "James E.J. Bottomley" <jejb@...ux.ibm.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 Hannes Reinecke <hare@...e.de>, Janek Kotas <jank@...ence.com>,
 Alim Akhtar <alim.akhtar@...sung.com>, Avri Altman <avri.altman@....com>,
 Bart Van Assche <bvanassche@....org>, Can Guo <quic_cang@...cinc.com>
Cc: Will Deacon <will@...nel.org>, linux-arm-msm@...r.kernel.org,
 linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v3 00/11] scsi: ufs: Remove overzealous memory
 barriers

On 21.12.2023 20:09, Andrew Halaney wrote:
> This is an RFC because I'm not all the confident in this topic. UFS has
> a lot of mb() variants used, most with comments saying "ensure this
> takes effect before continuing". mb()'s aren't really the way to
> guarantee that, a read back is the best method.
> 
> Some of these though I think could go a step further and remove the mb()
> variant without a read back. As far as I can tell there's no real reason
> to ensure it takes effect in most cases (there's no delay() or anything
> afterwards, and eventually another readl()/writel() happens which is by
> definition ordered).
If I understand this correctly - and I'm no expert - it's probably good
practice to read it back in critical places, so that if the code around
it changes, the most crucial writes arrive when expected.

Konrad