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

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Message-ID: <55B62782.9050701@citrix.com>
Date:	Mon, 27 Jul 2015 13:43:46 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<x86@...nel.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v2] xen/events: Support event channel rebind
 on ARM

On 27/07/15 13:35, David Vrabel wrote:
> 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.

My patch is based on Linus's master branch. Although, it has a
pre-requisite of [1] which I sent a few seconds before it. Though it's
only for applying because the 2 patches are not related.

I should have mentioned it in the mail, sorry.

> This also breaks the x86 build.

I forgot to test this new version when I turned the macro into a static
inline.

> /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).

Will resend a new version, and remove the dependency on [1].

Regards,

[1] http://permalink.gmane.org/gmane.linux.kernel/2004690

-- 
Julien Grall
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