linux-kernel - Re: [PATCH 11/11] KVM: MMU: improve write flooding detected

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Message-ID: <4E5656E6.1090204@redhat.com>
Date:	Thu, 25 Aug 2011 17:06:30 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 11/11] KVM: MMU: improve write flooding detected

On 08/25/2011 04:21 PM, Marcelo Tosatti wrote:
> On Thu, Aug 25, 2011 at 07:42:10AM +0300, Avi Kivity wrote:
> >  On 08/25/2011 05:04 AM, Marcelo Tosatti wrote:
> >  >>
> >  >>   It could increase the flood count independently of the accessed bit of
> >  >>   the spte being updated, zapping after 3 attempts as it is now.
> >  >>
> >  >>   But additionally reset the flood count if the gpte appears to be valid
> >  >>   (points to an existant gfn if the present bit is set, or if its zeroed).
> >  >
> >  >Well not zero, as thats a common pattern for non ptes.
> >  >
> >
> >  On 32-bit with 4GB RAM, practically anything is a valid gpte.
>
> The following could be required to consider a valid gpte, for write
> flood detection purposes:
>
> - Must be present.
> - PageCacheDisable must be unset.
> - PageWriteThrough must be unset.
>

Unless the guest is using PAT.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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