linux-kernel - Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs

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Date:	Tue, 12 Apr 2016 09:22:34 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Stefano Stabellini <sstabellini@...nel.org>,
	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	linux-kernel@...r.kernel.org, konrad.wilk@...cle.com,
	david.vrabel@...rix.com, jgross@...e.com
Subject: Re: Xen regression, Was: [PATCH] x86/irq: Probe for PIC presence
 before allocating descs for legacy IRQs

On 04/11/2016 10:08 PM, Stefano Stabellini wrote:
> Hi all,
>
> Unfortunately this patch (now commit
> 8c058b0b9c34d8c8d7912880956543769323e2d8) causes a regression on Xen
> when running on top of QEMU: the number of PIT irqs get set to 0 by
> probe_8259A but actually there are 16.
>
> Any suggestions on how to fix this?
>
> 1) we could revert 8c058b0b9c34d8c8d7912880956543769323e2d8
> 2) we could introduce an 'if (!xen_domain())' in probe_8259A
> 3) suggestions welcome

Stefano, do you have b4ff8389ed14b849354b59ce9b360bdefcdbf99c ?

It was supposed to fix this problem for Xen. However, I just noticed 
that arch/arm64/include/asm/irq.h makes nr_legacy_irqs() return 0 
(unlike arch/arm/include/asm/irq.h). Could that be the problem?


-boris