linux-kernel - Re: [kvm-devel] [PATCH][RFC] pte notifiers -- support for external page tables

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Message-ID: <46DF0EC2.7090408@qumranet.com>
Date:	Wed, 05 Sep 2007 23:17:06 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kvm-devel@...ts.sourceforge.net, general@...ts.openfabrics.org
Subject: Re: [kvm-devel] [PATCH][RFC] pte notifiers -- support for external
 page tables

Rusty Russell wrote:
> On Wed, 2007-09-05 at 22:32 +0300, Avi Kivity wrote:
>   
>> [resend due to bad alias expansion resulting in some recipients
>>  being bogus]
>>
>> Some hardware and software systems maintain page tables outside the normal
>> Linux page tables, which reference userspace memory.  This includes
>> Infiniband, other RDMA-capable devices, and kvm (with a pending patch).
>>     
>
> And lguest.  I can't tell until I've actually implemented it, but I
> think it will seriously reduce the need for page pinning which is why
> only root can currently launch guests.
>
>   

Ah yes, lguest.

> My concern is locking: this is called with the page lock held, and I
> guess we have to bump the guest out if it's currently running.
>   

This will complicate kvm's locking too.  We usually take kvm->lock to do 
mmu ops, but that is now a mutex.


-- 
Any sufficiently difficult bug is indistinguishable from a feature.

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