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

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Message-ID: <5050AB89.20705@redhat.com>
Date:	Wed, 12 Sep 2012 18:34:33 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Marcelo Tosatti <mtosatti@...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 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).


-- 
error compiling committee.c: too many arguments to function
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