RE: [Xen-devel] [PATCH] clflush instruction emulation

["Huang2, Wei" <Wei.Huang2@xxxxxxx>]

I can confirm that 21189 fixed FreeBSD issue.

Thanks,
-Wei

-----Original Message-----
From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx] 
Sent: Thursday, April 15, 2010 12:50 PM
To: Huang2, Wei
Cc: 'xen-devel@xxxxxxxxxxxxxxxxxxx'
Subject: Re: [Xen-devel] [PATCH] clflush instruction emulation

See what you think of xen-unstable:21189. It is also a bit more precise in
its decoding of CLFLUSH, as a member of Grp15.

 -- Keir

On 15/04/2010 18:32, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

> Our WBINVD emulation doesn't do anything unless the guest has some devices
> passed through to it. I think that will do for now then.
> 
>  Thanks,
>  Keir
> 
> On 15/04/2010 18:25, "Wei Huang" <wei.huang2@xxxxxxx> wrote:
> 
>> WBINVD is a bit heavy since it flushes all caches. I saw 1170 times of
>> CLFLUSH during FreeBSD booting. After guest boots, 0 was observed. 1170
>> is not huge though.
>> 
>> -Wei
>> 
>> Keir Fraser wrote:
>>> On 15/04/2010 17:38, "Wei Huang" <wei.huang2@xxxxxxx> wrote:
>>> 
>>>   
>>>> I created a patch which enables clflush emulation. I have verified that
>>>> this patch solves FreeBSD issue. This patch returns immediately without
>>>> doing anything. Note that we don't have to intercept clflush in SVM. So
>>>> the only time we have page_fault for clflush instruction is when guest
>>>> VM flushes MMIO space. In this case, do we need to send this command
>>>> over to QEMU? I didn't do it in this patch anyway.
>>>>     
>>> 
>>> I don't think we need to anything since all guest reads/writes to the mmio
>>> space will get intercepted to qemu, and hence qemu's view of the space is
>>> coherent with the guest with no need for special handling of CLFLUSH.
>>> 
>>> Still the emulator should call out and let the caller decide what to do. We
>>> could safely turn CLFLUSH into WBINVD (i.e., call the existing wbinvd hook).
>>> Do you know if these CLFLUSH emulations happen often or only very rarely?
>>> That might help us decide how smart we need to be about emulating CLFLUSH
>>> (i.e., add a hook specifically for clflush, separately from wbinvd).
>>> 
>>>  -- Keir
>>> 
>>> 
>>> 
>>>   
>> 
>> 
> 
> 
> 
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