linux-cve-announce - CVE-2021-47187: arm64: dts: qcom: msm8998: Fix CPU/L2 idle state latency and residency

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Message-ID: <2024041034-CVE-2021-47187-b158@gregkh>
Date: Wed, 10 Apr 2024 20:57:36 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47187: arm64: dts: qcom: msm8998: Fix CPU/L2 idle state latency and residency

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

arm64: dts: qcom: msm8998: Fix CPU/L2 idle state latency and residency

The entry/exit latency and minimum residency in state for the idle
states of MSM8998 were ..bad: first of all, for all of them the
timings were written for CPU sleep but the min-residency-us param
was miscalculated (supposedly, while porting this from downstream);
Then, the power collapse states are setting PC on both the CPU
cluster *and* the L2 cache, which have different timings: in the
specific case of L2 the times are higher so these ones should be
taken into account instead of the CPU ones.

This parameter misconfiguration was not giving particular issues
because on MSM8998 there was no CPU scaling at all, so cluster/L2
power collapse was rarely (if ever) hit.
When CPU scaling is enabled, though, the wrong timings will produce
SoC unstability shown to the user as random, apparently error-less,
sudden reboots and/or lockups.

This set of parameters are stabilizing the SoC when CPU scaling is
ON and when power collapse is frequently hit.

The Linux kernel CVE team has assigned CVE-2021-47187 to this issue.

Affected and fixed versions
===========================

	Fixed in 5.4.162 with commit a14d7038ea20
	Fixed in 5.10.82 with commit e52fecdd0c14
	Fixed in 5.15.5 with commit 118c826ef8b4
	Fixed in 5.16 with commit 3f1dcaff642e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47187
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	arch/arm64/boot/dts/qcom/msm8998.dtsi

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a14d7038ea201c5526375becfc43b9ba281b1e82
	https://git.kernel.org/stable/c/e52fecdd0c142b95c720683885b06ee3f0e065c8
	https://git.kernel.org/stable/c/118c826ef8b43efe0fda8faf419673707ee8c5e5
	https://git.kernel.org/stable/c/3f1dcaff642e75c1d2ad03f783fa8a3b1f56dd50