Date: Wed, 15 Jan 2014 19:38:07 +0100
From: Ingo Molnar <mingo@kernel.org>
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Borislav Petkov <bp@suse.de>, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org, aravind.gopalakrishnan@amd.com,
        tglx@linutronix.de, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86, cpu, amd: Add workaround for family 16h,
 erratum 793
Message-ID: <20140115183807.GA23486@gmail.com>
References: <20140114230711.GS29865@pd.tnic>
 <tip-3b56496865f9f7d9bcb2f93b44c63f274f08e3b6@git.kernel.org>
 <52D5DC51.9010606@zytor.com>
 <20140115062817.GA11869@gmail.com>
 <20140115133619.GA32051@pd.tnic>
 <52D69291.8080003@linux.intel.com>
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* H. Peter Anvin <hpa@linux.intel.com> wrote:

> On 01/15/2014 05:36 AM, Borislav Petkov wrote:
> >>
> >> msr_read() would essentially map to rdmsr_safe(). Each method has a
> >> return value that can be checked for failure.
> > 
> > I'm not sure we want to use the _safe() variants by default as it 
> > would generate the exception tables even in cases where they're 
> > clearly not needed.

I don't think those new methods should be inline functions - thus 
there will be only one exception entry for each.

> It would be particularly silly if what you end up with is in effect 
> to wrap msr_read/write() in a BUG_ON(), which is the effect of the 
> current (trapping) form.  There is something to be said for hard 
> errors.

Right, the fact that most of our MSR accesses today are 
crash-on-failure, which happens to trigger crashes on a regular 
schedule, where most of the crashes are 'harmless' situation except 
that they crash the systems for good.

So I think defaulting to soft failures is the right approach.

Thanks,

	Ingo
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