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

Avi Kivity
2007-09-05T20:17:06Z

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.