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

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Message-ID: <20120521193041.GA25940@amt.cnet>
Date:	Mon, 21 May 2012 16:30:41 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Gleb Natapov <gleb@...hat.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 04:15:50PM +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).

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