linux-kernel - Re: [PATCH v3 6/6] KVM: introduce readonly memslot

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Message-ID: <20120619072030.GM6533@redhat.com>
Date:	Tue, 19 Jun 2012 10:20:30 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 6/6] KVM: introduce readonly memslot

On Mon, Jun 18, 2012 at 05:25:05PM -0300, Marcelo Tosatti wrote:
> On Mon, Jun 18, 2012 at 12:50:10PM +0300, Avi Kivity wrote:
> > On 06/16/2012 05:11 AM, Marcelo Tosatti wrote:
> > > 
> > > Can you introduce a separate exit reason, say KVM_EXIT_READ_FAULT, with
> > > information about the fault?
> > 
> > I think you mean WRITE_FAULT.  
> 
> Yes.
> 
> > But what's wrong with the normal mmio exit?
> 
> It is necessary to perform an address->mmio region lookup, to verify
> whether the mmio exit is due to an actual mmio (no memory slot) or from
> a write access to a write protected slot. That information is readily
> available in the kernel but is lost if the mmio exit is used to transmit 
> the information.
> 
Why is it necessary though? Write access to a write protected slot is
MMIO by (our) definition.

> Moreover, i'd argue the uses are different: one is an mmio emulation
> exit, the other is more like handling a pagefault in qemu.
> 
What do you mean by "handling a pagefault in qemu"?

--
			Gleb.
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