linux-kernel - Re: [GIT PULL] x86/apic updates for v3.20

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Message-ID: <20150213154716.GG29106@8bytes.org>
Date:	Fri, 13 Feb 2015 16:47:16 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] x86/apic updates for v3.20

On Thu, Feb 12, 2015 at 06:08:45PM -0800, Linus Torvalds wrote:
> Any ideas? The Pixel Chromebook does have an odd and often broken
> BIOS/firmware thing, but it *used* to suspend and resume very reliably
> once we got around its insane TPM thing.

Hmm, looking at the patch and the surrounding code my guess is that
x2apic gets enabled now with 5fcee53ce705 on your Chromebook Pixel at
boot, which causes the suspend issue later for other reasons.

So the condition should rather look like this to keep x2apic disabled
like before:

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b665d24..770a0bb 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1580,8 +1580,8 @@ static __init void try_to_enable_x2apic(int remap_mode)
 		 * under KVM
 		 */
 		if (max_physical_apicid > 255 ||
-		    (IS_ENABLED(CONFIG_HYPERVISOR_GUEST) &&
-		     !hypervisor_x2apic_available())) {
+		    !(IS_ENABLED(CONFIG_HYPERVISOR_GUEST) &&
+		      hypervisor_x2apic_available())) {
 			pr_info("x2apic: IRQ remapping doesn't support X2APIC mode\n");
 			x2apic_disable();
 			return;

Another solution would be to just revert 5fcee53ce705. This code is not
in any fast-path, so we can live well without that optimization.


	Joerg

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