Re: [PATCH 5/6] kvm, x86: use ro page and don't copy shared page

Avi Kivity
2010-07-18T15:31:27Z

On 07/18/2010 06:23 PM, Gleb Natapov wrote:
> On Sun, Jul 18, 2010 at 06:14:11PM +0300, Avi Kivity wrote:
>
>> On 07/17/2010 07:31 AM, Gleb Natapov wrote:
>>
>>>>> Currently pages allocated for guest memory are required to be RW, so after your series
>>>>> behaviour will remain exactly the same as before.
>>>>>
>>>> Except KSM pages.
>>>>
>>>>
>>> KSM page will be COWed by __get_user_pages_fast(addr, 1, 1, page) in
>>> get_user_page_and_protection() just like it COWed now, no?
>>>
>> Well, we don't want to COW it on write faults.
>>

I meant read faults here.

>> The optimal behaviour is:
>>
>> - write faults: COW and instantiate a writeable spte
>>
> So do we or don't we want to COW on write faults?
>

We do (no choice).

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