linux-kernel - Re: [PATCH v6 12/12] KVM: indicate readonly access fault

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Message-ID: <20120912154452.GA19789@amt.cnet>
Date:	Wed, 12 Sep 2012 12:44:52 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v6 12/12] KVM: indicate readonly access fault

On Wed, Sep 12, 2012 at 06:34:33PM +0300, Avi Kivity wrote:
> On 09/11/2012 05:39 PM, Marcelo Tosatti wrote:
> > On Tue, Sep 11, 2012 at 12:18:22PM +0300, Avi Kivity wrote:
> >> > The same can happen with slot deletion, for example. 
> >> > 
> >> > Userspace (which performed the modification which can result in faults
> >> > to non-existant/read-only/.../new-tag memslot), must handle the faults 
> >> > properly or avoid the possibility for reference to memslot information 
> >> > from the past.
> >> > 
> >> > I think its worthwhile to add a note about this in the API
> >> > documentation: "The user of this interface is responsible for handling 
> >> > references to stale memslot information, either by handling
> >> > exit notifications which reference stale memslot information or not
> >> > allowing these notifications to exist by stopping all vcpus in userspace
> >> > before performing modifications to the memslots map".
> >> 
> >> Or we can drop the new interface and rely on userspace to perform the
> >> lookup under its own locking rules.
> >> 
> >> It's slow, but writes to ROM or ROM/device are rare anyway.
> > 
> > Lookup what information? 
> 
> Where to dispatch the write.
> 
> In fact userspace has to do that anyway if it's a ROM/device.  There's
> no way userspace can guess that unless we pass in the slot number (which
> isn't synchronized with anything).

Alright, do you prefer the details of this exit to be worked out later,
when necessary, then? 

That is, not merge this particular patch of the series? 

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