linux-kernel - Re: [PATCH 3/4] Add the code to send the consigned time from the host to the guest

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Message-ID: <5113B9AF.5040109@linux.vnet.ibm.com>
Date:	Thu, 07 Feb 2013 08:26:55 -0600
From:	Michael Wolf <mjw@...ux.vnet.ibm.com>
To:	Rik van Riel <riel@...hat.com>
CC:	linux-kernel@...r.kernel.org, gleb@...hat.com, kvm@...r.kernel.org,
	peterz@...radead.org, mtosatti@...hat.com, glommer@...allels.com,
	mingo@...hat.com, anthony@...emonkey.ws
Subject: Re: [PATCH 3/4] Add the code to send the consigned time from the
 host to the guest

On 02/06/2013 03:18 PM, Rik van Riel wrote:
> On 02/05/2013 04:49 PM, Michael Wolf wrote:
>> Change the paravirt calls that retrieve the steal-time information
>> from the host.  Add to it getting the consigned value as well as
>> the steal time.
>>
>> Signed-off-by: Michael Wolf <mjw@...ux.vnet.ibm.com>
>
>> diff --git a/arch/x86/include/uapi/asm/kvm_para.h 
>> b/arch/x86/include/uapi/asm/kvm_para.h
>> index 06fdbd9..55d617f 100644
>> --- a/arch/x86/include/uapi/asm/kvm_para.h
>> +++ b/arch/x86/include/uapi/asm/kvm_para.h
>> @@ -42,9 +42,10 @@
>>
>>   struct kvm_steal_time {
>>       __u64 steal;
>> +    __u64 consigned;
>>       __u32 version;
>>       __u32 flags;
>> -    __u32 pad[12];
>> +    __u32 pad[10];
>>   };
>
> The function kvm_register_steal_time passes the address of such
> a structure to the host kernel, which then does something with
> it.
>
> Could running a guest with the above patch, on top of a host
> with the old code, result in the values for "version" and
> "flags" being written into "consigned"?
yes, good point.
>
> Could that result in confusing the guest kernel to no end,
> and generally breaking things?
>
Ok I will move the consigned field to be after the flags.

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