From: Gleb Natapov <gleb@redhat.com>
To: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Cc: Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH v3 2/3] KVM: MMU: fix accessed bit set on prefault path
Date: Tue, 30 Nov 2010 20:38:33 +0200 [thread overview]
Message-ID: <20101130183833.GB2924@redhat.com> (raw)
In-Reply-To: <4CF53F41.1040503@cn.fujitsu.com>
On Wed, Dec 01, 2010 at 02:15:29AM +0800, Xiao Guangrong wrote:
> On 12/01/2010 01:50 AM, Gleb Natapov wrote:
> > On Wed, Dec 01, 2010 at 12:52:22AM +0800, Xiao Guangrong wrote:
> >> On 11/30/2010 09:29 PM, Gleb Natapov wrote:
> >>
> >>>> + if (!shadow_accessed_mask)
> >>>> + return;
> >>>> +
> >>> I don't get this. As far as I can see VMX inits shadow_accessed_mask to
> >>> be zero if ept is enabled. This line here means that we never prefault with ept
> >>> enabled. It is opposite from what it should be.
> >>>
> >>
> >> Since it's no accessed bit on EPT, it's no way to distinguish between actually
> >> accessed translations and prefault.
> > Why is this a problem? We do what this page to not be evicted again
> > since we expect it to be accessed.
> >
>
> It can't avoid the page to be evicted again since the page is marked accessed only
> when spte is droped or updated.
I still do not understand why are you disabling prefault for ept. Why
do you want to distinguish between actually accessed translations and
prefauls? What problem are you trying to fix?
--
Gleb.
next prev parent reply other threads:[~2010-11-30 18:38 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-30 9:34 [PATCH v3 1/3] KVM: MMU: rename 'no_apf' to 'prefault' Xiao Guangrong
2010-11-30 9:36 ` [PATCH v3 2/3] KVM: MMU: fix accessed bit set on prefault path Xiao Guangrong
2010-11-30 13:29 ` Gleb Natapov
2010-11-30 16:52 ` Xiao Guangrong
2010-11-30 17:50 ` Gleb Natapov
2010-11-30 18:15 ` Xiao Guangrong
2010-11-30 18:38 ` Gleb Natapov [this message]
2010-11-30 19:11 ` Xiao Guangrong
2010-11-30 19:20 ` Gleb Natapov
2010-12-01 2:20 ` Xiao Guangrong
2010-12-01 20:42 ` Marcelo Tosatti
2010-11-30 9:37 ` [PATCH v3 3/3] KVM: MMU: retry #PF for softmmu Xiao Guangrong
2010-12-02 1:19 ` Marcelo Tosatti
2010-12-02 3:44 ` Xiao Guangrong
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