linux-kernel - Re: [PATCH v2] xen/events: Support event channel rebind on ARM

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Date:	Mon, 27 Jul 2015 13:35:20 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Julien Grall <julien.grall@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	"Catalin Marinas" <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	<x86@...nel.org>
Subject: Re: [PATCH v2] xen/events: Support event channel rebind on ARM

On 27/07/15 12:35, Julien Grall wrote:
> Currently, the event channel rebind code is gated with the presence of
> the vector callback.
> 
> The virtual interrupt controller on ARM has the concept of per-CPU
> interrupt (PPI) which allow us to support per-VCPU event channel.
> Therefore there is no need of vector callback for ARM.
> 
> Xen is already using a free PPI to notify the guest VCPU of an event.
> Furthermore, the xen code initialization in Linux (see
> arch/arm/xen/enlighten.c) is requesting correctly a per-CPU IRQ.
> 
> Introduce new helper xen_support_evtchn_rebind to allow architecture
> decide whether rebind an event is support or not. It will always return
> 1 on ARM and keep the same behavior on x86.
> 
> This is also allow us to drop the usage of xen_have_vector_callback
> entirely in the ARM code.

This did not apply cleanly.  Please always base patches on Linus's
master branch.

This also breaks the x86 build.

/local/davidvr/work/k.org/tip/arch/x86/include/asm/xen/events.h: In
function ‘xen_support_evtchn_rebind’:
/local/davidvr/work/k.org/tip/arch/x86/include/asm/xen/events.h:29:85:
error: ‘xen_have_vector_callback’ undeclared (first use in this function)
  return (!xen_hvm_domain() || xen_have_vector_callback);

> --- a/arch/arm/include/asm/xen/events.h
> +++ b/arch/arm/include/asm/xen/events.h
> @@ -20,4 +20,10 @@ static inline int xen_irqs_disabled(struct pt_regs *regs)
>  							    atomic64_t,	\
>  							    counter), (val))
>  
> +/* Rebind event channel is supported by default */
> +static inline bool xen_support_evtchn_rebind(void)
> +{
> +	return 1;

This should be true (similarly for arm64).

David
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