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Re: [Xen-devel] [PATCH 3/5] vtdt: Modify vlapic code to add vtdt support
- To: "Wei, Gang" <gang.wei@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
- From: Keir Fraser <keir@xxxxxxx>
- Date: Tue, 14 Dec 2010 08:48:51 +0000
- Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
- Delivery-date: Tue, 14 Dec 2010 00:49:38 -0800
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- Thread-topic: [Xen-devel] [PATCH 3/5] vtdt: Modify vlapic code to add vtdt support
On 14/12/2010 08:22, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:
>>> @@ -265,6 +265,7 @@ struct hvm_hw_lapic {
>>> uint64_t apic_base_msr;
>>> uint32_t disabled; /* VLAPIC_xx_DISABLED */
>>> uint32_t timer_divisor;
>>> + uint64_t tdt_msr;
>>> };
>>
>> Is this backward compatible with old HVM save images?
>
> I am not sure about this. If it isn't, would you accept to simply add another
> data trunk for TDT msr?
That's Tim's call. I would personally prefer for Xen to accept truncated
chunks, and extend them with sensible 'old save image' defaults, such as
all-zeroes. That would be a generic solution to this case which will be
reusable in future, and avoid needlessly creating extra chunk types just for
backward compatibility reasons.
-- Keir
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