linux-kernel - Re: [GIT PULL] x86/apic changes for v3.14

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Date:	Mon, 24 Mar 2014 10:24:37 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86/apic changes for v3.14


* Maciej W. Rozycki <macro@...ux-mips.org> wrote:

> IMPLICATION: There is a possibility of clearing the Error register 
> status since the write to the register is not specifically blocked.
> 
> WORKAROUND: Writes should not occur to the Pentium processor APIC 
> Error register.
> 
> STATUS: For the steppings affected see the Summary Table of Changes 
> at the beginning of this section."
> 
> The steppings affected are actually: B1, B3 and B5.  Do we want to 
> keep supporting them?  I think yes, we already handle the erratum 
> elsewhere (lapic_setup_esr).  So how about:
> 
> 	if (lapic_get_maxlvt() > 3)	/* Due to the Pentium erratum 3AP. */
> 		apic_write(APIC_ESR, 0);
> 	v = apic_read(APIC_ESR);
> 
> instead?  I can make a patch if that would make your life easier.

Sure, a patch would be helpful.

>  There's room for optimisation here, but I think it's not worth the 
> effort as this is a slow path, APIC error interrupts are not 
> supposed to happen and are I believe extremely uncommon with FSB 
> message delivery.

Agreed.

Thanks,

	Ingo
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