linux-kernel - Re: [PATCH v2 10/16] KVM: MMU: fask check whether page is writable

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Message-ID: <4F8D1EB5.2000302@redhat.com>
Date:	Tue, 17 Apr 2012 10:41:41 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 10/16] KVM: MMU: fask check whether page is writable

On 04/17/2012 06:55 AM, Xiao Guangrong wrote:
> On 04/16/2012 07:47 PM, Avi Kivity wrote:
>
> > On 04/16/2012 01:20 PM, Xiao Guangrong wrote:
> >>>>
> >>>> It is used to avoid the unnecessary overload 
> >>>
> >>> It's overloading me :(
> >>>
> >>
> >>
> >> Sorry.
> >>
> > 
> > The trick is to send those in separate patchset so the maintainer
> > doesn't notice.
> > 
>
>
> Thanks for your suggestion, i will pay more attention on it in the
> further.
>
> For this patch, what did you mean of "those"? You mean the whole
> rmap.PTE_LIST_WP_BIT (fast check for shadow page table write protection
> and host write protection) or just about host_page_write_protect
> (for KSM only)?

All of it.  Let's start with just modifying sptes concurrently and only
later add reading bits from rmap concurrently, if it proves necessary.

>
> If we do not have rmap.PTE_LIST_WP_BIT, there may have regression on
> shadow mmu.
>
> Hmm, do i need implement rmap.PTE_LIST_WP_BIT, then fast page fault?

Let's try to measure the effect without rmap.PTE_LIST_WP_BIT.  Usually
PTE chains for page tables are short so the effect would be small.  Of
course we can't tell about all guest.

-- 
error compiling committee.c: too many arguments to function

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