linux-kernel - Re: [PATCH v2 2/6] KVM: MMU: don't drop spte if overwrite it from W to RO

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Message-ID: <4CE5573E.4050100@redhat.com>
Date:	Thu, 18 Nov 2010 18:41:34 +0200
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 v2 2/6] KVM: MMU: don't drop spte if overwrite it from
 W to RO

On 11/18/2010 05:32 PM, Marcelo Tosatti wrote:
> >  >>  There is no need to flush on sync_page path since the guest is
> >  >>  responsible for it.
> >  >>
> >  >
> >  >   If we don't, the next rmap_write_protect() will incorrectly decide that
> >  >  there's no need to flush tlbs.
> >  >
> >
> >  Maybe it's not a problem if guest can flush all tlbs after overwrite it?
> >  Marcelo, what's your comment about this?
>
> It can, but there is no guarantee. Your patch is correct.

We keep tripping on the same problem again and again.  spte.w (and 
tlb.pte.w) is multiplexed between guest and host, hence we cannot trust 
the guest regarding its consistency.

I wish we had a systematic way of dealing with this.

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

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