linux-kernel - Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked

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Message-ID: <4F6A2832.9080306@codemonkey.ws>
Date:	Wed, 21 Mar 2012 14:12:50 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	Avi Kivity <avi@...hat.com>
CC:	Jan Kiszka <jan.kiszka@...mens.com>,
	Gleb Natapov <gleb@...hat.com>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Northup <digitaleric@...gle.com>,
	kvm list <kvm@...r.kernel.org>,
	Amit Shah <amit.shah@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [Qemu-devel] [PATCH 0/2 v3] kvm: notify host when guest panicked

On 03/15/2012 06:46 AM, Avi Kivity wrote:
> On 03/15/2012 01:25 PM, Jan Kiszka wrote:
>>>>
>>> There was such vm exit (KVM_EXIT_HYPERCALL), but it was deemed to be a
>>> bad idea.
>>
>> BTW, this would help a lot in emulating hypercalls of other hypervisors
>> (or of KVM's VAPIC in the absence of in-kernel irqchip - I had to jump
>> through hoops therefore) in user space. Not all those hypercall handlers
>> actually have to reside in the KVM module.
>>
>
> That is true.  On the other hand the hypercall ABI might go to pieces if
> there was no central implementation.

Just declare that outl 0x505 is a megaultracall and s/vmcall/outb/g and call it 
a day.

The performance difference between vmcall and outl is so tiny compared to the 
cost of dropping to userspace that it really doesn't matter which instruction is 
used.

Regards,

Anthony Liguori

>

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