Re: [PATCH] KVM: x86: Add instruction length to VCPU event state

[Jan Kiszka <jan.kiszka@web.de>]

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Gleb Natapov wrote:
> On Sat, Feb 13, 2010 at 06:49:44PM +0100, Jan Kiszka wrote:
>> Gleb Natapov wrote:
>>> On Sat, Feb 13, 2010 at 10:51:40AM +0100, Jan Kiszka wrote:
>>>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>>>
>>>> VMX requires a properly set instruction length VM entry field when
>>>> trying to inject soft exception and interrupts. We have to preserve this
>>>> state across VM save/restore to avoid breaking the re-injection of such
>>>> events on Intel. So add it to the new VCPU event state.
>>>>
>>> We shouldn't re-inject soft exceptions/interrupts after migration, but
>>> re-execute instruction instead. Instruction length field doesn't exist
>>> on SVM and migration shouldn't expose implementation details.
>>>
>> Hmm, then I guess this totally untested patch should fly:
>>
> I don't understand what problem are you trying to solve by your patch.
> During normal operation event_exit_inst_len will be set to correct
> value. After migration rip will point to int instruction an no even will
> be pending at all. Here is the patch:

The patch will cause an endless loop if BP interception is enabled.

What is the purpose of keeping event_exit_inst_len around? Either we
need it also across user space exists, then we have to save/restore or
reconstruct it, or we don't need it, then simply drop it.

Jan


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