linux-kernel - Re: [kvm-devel] [PATCH 2/3] Refactor hypercall infrastructure (v3)

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Message-ID: <46EFCED0.5050209@qumranet.com>
Date:	Tue, 18 Sep 2007 15:12:48 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Anthony Liguori <aliguori@...ibm.com>
CC:	kvm-devel@...ts.sourceforge.net, Zachary Amsden <zach@...are.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH 2/3] Refactor hypercall infrastructure (v3)

Avi Kivity wrote:
> Anthony Liguori wrote:
>   
>> This patch refactors the current hypercall infrastructure to better support live
>> migration and SMP.  It eliminates the hypercall page by trapping the UD
>> exception that would occur if you used the wrong hypercall instruction for the
>> underlying architecture and replacing it with the right one lazily.
>>
>> It also introduces the infrastructure to probe for hypercall available via
>> CPUID leaves 0x40000000.  CPUID leaf 0x40000001 should be filled out by
>> userspace.
>>
>> A fall-out of this patch is that the unhandled hypercalls no longer trap to
>> userspace.  There is very little reason though to use a hypercall to communicate
>> with userspace as PIO or MMIO can be used.  There is no code in tree that uses
>> userspace hypercalls.
>>
>>   
>>     
>
>
> Surprisingly, this patch kills Windows XP (ACPI HAL).  I'll try to find 
> out why.
>
>   

Not trapping #UD brings things back to normal.  So, Windows likes to 
execute undefined instructions, and we don'd handle these well.

I really should start asking for unit tests for these kinds of things 
(execute undefined instruction, see the #UD, say ok).

-- 
error compiling committee.c: too many arguments to function

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