linux-kernel - Re: [PATCH] x86: prevent unconditional writes to DebugCtl MSR

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Message-ID: <87r6ei8tds.fsf@basil.nowhere.org>
Date:	10 Mar 2008 16:56:47 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Jan Beulich" <jbeulich@...ell.com>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>,
	<markus.t.metzger@...el.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: prevent unconditional writes to DebugCtl MSR

"Jan Beulich" <jbeulich@...ell.com> writes:
>  
> +static inline void update_debugctlmsr(unsigned long debugctlmsr)
> +{
> +#ifndef CONFIG_X86_DEBUGCTLMSR
> +	if (boot_cpu_data.x86 < 6)
> +		return;
> +#endif
> +	wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr);

It would be better to use checking_wrmsrl() instead of the model
check because often VMs etc. are missing such MSRs too, but 
report the higher family number.

Also silently failing is not very nice, but that's a different issue.

-Andi
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