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From: Thomas Gleixner <tglx@linutronix.de>
To: Benjamin Lamowski <benjamin.lamowski@kernkonzept.com>,
	xiaoyao.li@intel.com
Cc: philipp.eppelt@kernkonzept.com, bp@alien8.de,
	fenghua.yu@intel.com, hpa@zytor.com,
	linux-kernel@vger.kernel.org, luto@kernel.org, mingo@redhat.com,
	nivedita@alum.mit.edu, pbonzini@redhat.com, peterz@infradead.org,
	sean.j.christopherson@intel.com, tony.luck@intel.com,
	x86@kernel.org
Subject: Re: [PATCH 0/1] x86/split_lock: check split lock feature on initialization
Date: Mon, 06 Apr 2020 23:21:13 +0200	[thread overview]
Message-ID: <87369gl392.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200403174403.306363-1-benjamin.lamowski@kernkonzept.com>

Benjamin Lamowski <benjamin.lamowski@kernkonzept.com> writes:
> 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.

No. It's not an oversight, it's a simplification and it's perfectly
legit. rdsmrl_safe() on a unimplemented MSR results in a #GP which is
caught and fixed up. Nothing to see here.

Thanks,

        tglx

      parent reply	other threads:[~2020-04-06 21:21 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-25  3:09 [PATCH v7 0/2] Fix and optimization of split_lock_detection Xiaoyao Li
2020-03-25  3:09 ` [PATCH v7 1/2] x86/split_lock: Rework the initialization flow of split lock detection Xiaoyao Li
2020-03-28 16:32   ` Sean Christopherson
2020-03-30 13:26     ` Xiaoyao Li
2020-03-30 14:26       ` Sean Christopherson
2020-03-25  3:09 ` [PATCH v7 2/2] x86/split_lock: Avoid runtime reads of the TEST_CTRL MSR Xiaoyao Li
2020-03-28 16:34   ` Sean Christopherson
2020-03-29  9:13     ` Xiaoyao Li
2020-03-30 18:18       ` Sean Christopherson
2020-04-03 17:44 ` [PATCH 0/1] x86/split_lock: check split lock feature on initialization Benjamin Lamowski
2020-04-03 17:44   ` [PATCH 1/1] " Benjamin Lamowski
2020-04-03 18:01     ` Sean Christopherson
2020-04-06  8:23       ` Benjamin Lamowski
2020-04-06 11:48         ` Xiaoyao Li
2020-04-06 15:57           ` [PATCH v2 0/1] x86/split_lock: check split lock support " Benjamin Lamowski
2020-04-06 16:02             ` [PATCH v2 1/1] " Benjamin Lamowski
2020-04-06 16:17               ` [PATCH v3 " Benjamin Lamowski
2020-04-06 21:24                 ` Thomas Gleixner
2020-04-06 21:21   ` Thomas Gleixner [this message]

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