linux-kernel - Re: [PATCH v2 5/5] KVM: MMU: retry #PF for softmmu

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Message-ID: <20101115095651.GI7948@redhat.com>
Date:	Mon, 15 Nov 2010 11:56:51 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] KVM: MMU: retry #PF for softmmu

On Mon, Nov 15, 2010 at 05:55:25PM +0800, Xiao Guangrong wrote:
> On 11/15/2010 05:30 PM, Avi Kivity wrote:
> 
> >> Yeah, this 'retry' is unnecessary if the process is killed, but this
> >> case is infrequent, the most case is the process keeps running and try
> >> to access the fault address later.
> > 
> > The problem is that if we retry in this case, we install an incorrect spte?
> > 
> 
> ......
> 
> >> can avoid if the page mapping have been fixed.
> > 
> > The guest may have changed page directories or other levels.
> > 
> 
> ......
> 
> >> >  Or another thread may have mmap()ed something else over the
> >> >  same address.
> >>
> >> The mmap virtual address is also visible for other threads since the
> >> threads
> >> have the same page table, so i think this case is the same as above?
> > 
> > Again, don't we install the wrong spte in this case?
> > 
> 
> I think it doesn't corrupts spte since we will walk guest page table again
> and map it to shadow pages when we retry #PF.
But if the page is not mapped by new process we can inject #PF into a
guest.

--
			Gleb.
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