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Date: Mon, 16 Feb 2015 08:22:04 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Joerg Roedel <joro@8bytes.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Jiang Liu <jiang.liu@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] x86/apic updates for v3.20
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* Joerg Roedel <joro@8bytes.org> wrote:

> 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;

Indeed!

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

Agreed.

Thanks,

	Ingo