linux-kernel - Re: The msr_safe functions and returning -EFAULT

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Message-ID: <4A9C6A74.3070706@zytor.com>
Date:	Mon, 31 Aug 2009 17:27:32 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Avi Kivity <avi@...ranet.com>
Subject: Re: The msr_safe functions and returning -EFAULT

On 08/31/2009 05:24 PM, Jeremy Fitzhardinge wrote:
> On 08/30/09 14:05, H. Peter Anvin wrote:
>> Right now, the *msr_safe() functions are returning -EFAULT.  As far as I
>> can tell, this makes absolutely no sense -- EFAULT is a nonsensical
>> error (it means a pointer into user memory given to a system call is
>> invalid), and the only user that seems to use this as anything other
>> than a boolean is the MSR driver, which wants EIO.
>>
>> Sending out an email in case I have missed any instances, but I'm
>> inclined to just change this to EIO globally.
>>
>> Anyone has objections?
>>   
> 
> I think the only rationale for EFAULT is that the *msr will fail with
> GP, and a GPing instruction will send a SIGSEGV to usermode, and EFAULT
> is the synchronous error-code equiv of SIGSEGV.  Sorta.
> 
> EIO makes more sense overall.  Or ENXIO.

Well, EIO is what we want for the MSR driver, so I have just switched it
to EIO across the board.  As far as I can tell, there were no other
users that didn't just test for error or no error.

	-hpa


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