linux-kernel - [PATCH RFC v3 10/11] scsi: ufs: core: Perform read back to commit doorbell

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: <20231221-ufs-reset-ensure-effect-before-delay-v3-10-2195a1b66d2e@redhat.com>
Date: Thu, 21 Dec 2023 13:09:56 -0600
From: Andrew Halaney <ahalaney@...hat.com>
To: Andy Gross <agross@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.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: Andrew Halaney <ahalaney@...hat.com>,
	Will Deacon <will@...nel.org>,
	linux-arm-msm@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH RFC v3 10/11] scsi: ufs: core: Perform read back to commit doorbell

Currently, the doorbell is written to and a wmb() is used to commit it
immediately.

wmb() ensures that the write completes before following writes occur,
but completion doesn't mean that it isn't stored in a buffer somewhere.
The recommendation for ensuring this bit has taken effect on the device
is to perform a read back to force it to make it all the way to the
device. This is documented in device-io.rst and a talk by Will Deacon on
this can be seen over here:

    https://youtu.be/i6DayghhA8Q?si=MiyxB5cKJXSaoc01&t=1678

Let's do that to ensure the bit hits the device. Because the wmb()'s
purpose wasn't to add extra ordering (on top of the ordering guaranteed
by writel()/readl()), it can safely be removed.

Fixes: ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the doorbell")
Signed-off-by: Andrew Halaney <ahalaney@...hat.com>
---
 drivers/ufs/core/ufshcd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 75a03ee9a1ba..caebd589e08c 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -7050,7 +7050,7 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba,
 
 	ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL);
 	/* Make sure that doorbell is committed immediately */
-	wmb();
+	ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL);
 
 	spin_unlock_irqrestore(host->host_lock, flags);
 

-- 
2.43.0