linux-kernel - [PATCH 0/1] x86/split_lock: check split lock feature on initialization

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Message-Id: <20200403174403.306363-1-benjamin.lamowski@kernkonzept.com>
Date:   Fri,  3 Apr 2020 19:44:02 +0200
From:   Benjamin Lamowski <benjamin.lamowski@...nkonzept.com>
To:     xiaoyao.li@...el.com
Cc:     philipp.eppelt@...nkonzept.com, bp@...en8.de, fenghua.yu@...el.com,
        hpa@...or.com, linux-kernel@...r.kernel.org, luto@...nel.org,
        mingo@...hat.com, nivedita@...m.mit.edu, pbonzini@...hat.com,
        peterz@...radead.org, sean.j.christopherson@...el.com,
        tglx@...utronix.de, tony.luck@...el.com, x86@...nel.org
Subject: [PATCH 0/1] x86/split_lock: check split lock feature on initialization

Hi,

During regression testing of our hypervisor[1] with the current git tip,
we got writes to the TEST_CTRL MSR on hardware that does not support
split lock detection. While the original split_lock implementation does
not exhibit this behavior, the reworked initialization from
dbaba47085b0c unconditionally calls split_lock_verify_msr() from
split_lock_init().

After the elaborate checks in cpu_set_core_cap_bits() this seems like an
oversight. The following simple patch fixes our regression by checking
for X86_FEATURE_SPLIT_LOCK_DETECT before accessing the TEST_CTRL MSR.

Please CC me on replies - I am not subscribed to the LKML.

Kind regards,

Ben

[1] https://github.com/kernkonzept/uvmm

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Benjamin Lamowski - +49.351.41883235
Operating Systems Engineer - https://www.kernkonzept.com

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