linux-kernel - [PATCH v2 0/1] x86/split_lock: check split lock support on initialization

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Message-Id: <20200406155743.206444-1-benjamin.lamowski@kernkonzept.com>
Date:   Mon,  6 Apr 2020 17:57:42 +0200
From:   Benjamin Lamowski <benjamin.lamowski@...nkonzept.com>
To:     xiaoyao.li@...el.com
Cc:     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,
        philipp.eppelt@...nkonzept.com, sean.j.christopherson@...el.com,
        tglx@...utronix.de, tony.luck@...el.com, x86@...nel.org
Subject: [PATCH v2 0/1] x86/split_lock: check split lock support on initialization

> It's for the case that SLD is explicitly disabled by kernel params
> "split_lock_detect=off". You know, BIOS may turn SLD on for itself. So
> if user uses "split_lock_detect=off", we have to clear the SLD bit in
> case BIOS forgets to clear it.

Ah, I forgot that split_lock_setup() returns early if sld is disabled.
Thanks for explaining!

[...]
> If you really want to avoid the MSR access on the platform without SLD.
> You could make the default sld_state as sld_unsupported. It can only be
> changed to other value in split_lock_setup() when SLD is enumerated. So
> in split_lock_init(), we can use if (sld_state == sld_unsupported) to
> skip the MSR_TEST_CTRL access.

Attached is a new version of my patch that implements your suggestion.

Thanks,

Ben

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