linux-kernel - Re: [PATCH] KVM: fix async page fault working for readonly mapping

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Message-ID: <20120522053110.GT10209@redhat.com>
Date:	Tue, 22 May 2012 08:31:10 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Avi Kivity <avi@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH] KVM: fix async page fault working for readonly mapping

On Mon, May 21, 2012 at 04:30:41PM -0300, Marcelo Tosatti wrote:
> On Mon, May 21, 2012 at 04:15:50PM +0800, Xiao Guangrong wrote:
> > On 05/21/2012 04:08 PM, Gleb Natapov wrote:
> > 
> > > On Mon, May 21, 2012 at 02:45:45PM +0800, Xiao Guangrong wrote:
> > >> If we map a readonly memory space from host to guest and the page is
> > >> not currently mapped in the host, we will get a fault-pfn and async
> > >> is not allowed, then the vm will crash
> > >>
> > > Why would we want to map a readonly memory space from host to guest?
> > > We may want to do it to support memory semantics on read and mmio on
> > > write, but do not right now unless something changed while I was not
> > > looking.
> > 
> > 
> > Some test cases in kvm-unit-tests and the benchmark i am writing for KVM
> > need map the function on host to guest.
> 
> Or ROM. Or read-only mappings of IVSHMEM (which don't exist yet).
True. KVM should ignore writes to such areas, not kill a guest. Is this
how the code works today?

--
			Gleb.
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