Re: [Xen-devel] [XEN PATCH v1 1/1] x86/vm_event: add fast single step

[Ковалёв Сергей <valor@xxxxxxx>]

Andrew, Tamas thank you very much. I will improve the patch.

December 17, 2019 3:13:42 PM UTC, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 
пишет:
>On 17/12/2019 15:10, Tamas K Lengyel wrote:
>> On Tue, Dec 17, 2019 at 8:08 AM Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
>wrote:
>>> On Tue, Dec 17, 2019 at 7:48 AM Andrew Cooper
><andrew.cooper3@xxxxxxxxxx> wrote:
>>>> On 17/12/2019 14:40, Sergey Kovalev wrote:
>>>>> On break point event eight context switches occures.
>>>>>
>>>>> With fast single step it is possible to shorten path for two
>context
>>>>> switches
>>>>> and gain 35% spead-up.
>>>>>
>>>>> Was tested on Debian branch of Xen 4.12. See at:
>>>>>
>https://github.com/skvl/xen/tree/debian/knorrie/4.12/fast-singlestep
>>>>>
>>>>> Rebased on master:
>>>>> https://github.com/skvl/xen/tree/fast-singlestep
>>>>>
>>>>> Signed-off-by: Sergey Kovalev <valor@xxxxxxx>
>>>> 35% looks like a good number, but what is "fast single step"?  All
>this
>>>> appears to be is plumbing for to cause an altp2m switch on single
>step.
>>> Yes, a better explanation would be much needed here and I'm not 100%
>>> sure it correctly implements what I think it tries to.
>>>
>>> This is my interpretation of what the idea is: when using DRAKVUF
>(or
>>> another system using altp2m with shadow pages similar to what I
>>> describe in
>https://xenproject.org/2016/04/13/stealthy-monitoring-with-xen-altp2m),
>>> after a breakpoint is hit the system switches to the default
>>> unrestricted altp2m view with singlestep enabled. When the
>singlestep
>>> traps to Xen another vm_event is sent to the monitor agent, which
>then
>>> normally disables singlestepping and switches the altp2m view back
>to
>>> the restricted view. This patch looks like its short-circuiting that
>>> last part so that it doesn't need to send the vm_event out for the
>>> singlestep event and should switch back to the restricted view in
>Xen
>>> automatically. It's a nice optimization. But what seems to be
>missing
>>> is the altp2m switch itself.
>> Never mind, p2m_altp2m_check does the altp2m switch as well, so this
>> patch implements what I described above. Please update the patch
>> message to be more descriptive (you can copy my description from
>> above).
>
>Also please read CODING_STYLE in the root of the xen repository.  The
>important ones you need to fix are spaces in "if ( ... )" statements,
>and binary operators on the end of the first line rather than the
>beginning of the continuation.
>
>~Andrew

-- 
Простите за краткость, создано в K-9 Mail.

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