linux-kernel - Re: [PART1 RFC v2 07/10] svm: Add VMEXIT handlers for AVIC

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Date:	Thu, 17 Mar 2016 10:58:07 +0700
From:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
To:	Radim Krčmář <rkrcmar@...hat.com>
CC:	<pbonzini@...hat.com>, <joro@...tes.org>, <bp@...en8.de>,
	<gleb@...nel.org>, <alex.williamson@...hat.com>,
	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<wei@...hat.com>, <sherry.hurwitz@....com>
Subject: Re: [PART1 RFC v2 07/10] svm: Add VMEXIT handlers for AVIC

Hi Radim,

On 03/10/2016 03:55 AM, Radim Krčmář wrote:
>> >+	pr_debug("%s: offset=%#x, rw=%#x, vector=%#x, vcpu_id=%#x, cpu=%#x\n",
>> >+		 __func__, offset, rw, vector, svm->vcpu.vcpu_id, svm->vcpu.cpu);
>> >+
>> >+	BUG_ON(offset >= 0x400);
> These are valid faulting registers, so our implementation has to handle
> them.  (And the rule is to never BUG if a recovery is simple.)
>

Just want to clarify the part that you mentioned "to handle them". 
IIUC, offet 0x400 and above are for x2APIC stuff, which AVIC does not 
currently support. Also, since I have only advertised as xAPIC when 
enabling AVIC, if we run into the situation that the VM is trying to 
access these register, we should just ignore it (and not BUG). Do I 
understand that correctly?

Thanks,
Suravee