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Re: [Qemu-devel] [PATCH v1 2/2] intel-iommu: Extend address width to 48
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [PATCH v1 2/2] intel-iommu: Extend address width to 48 bits |
Date: |
Thu, 30 Nov 2017 11:25:51 +0800 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Wed, Nov 29, 2017 at 01:05:22PM -0800, Prasad Singamsetty wrote:
> Thanks Michael. Some comments below.
>
> On 11/28/2017 9:32 AM, Michael S. Tsirkin wrote:
> > On Tue, Nov 14, 2017 at 06:13:50PM -0500, address@hidden wrote:
> > > From: Prasad Singamsetty <address@hidden>
> > >
> > > The current implementation of Intel IOMMU code only supports 39 bits
> > > iova address width. This patch provides a new parameter (x-aw-bits)
> > > for intel-iommu to extend its address width to 48 bits but keeping the
> > > default the same (39 bits). The reason for not changing the default
> > > is to avoid potential compatibility problems
> >
> > You can change the default, just make it 39 for existing machine types.
>
> I think introducing a new machine type is not appropriate as this
> is an implementation limitation for the existing machine type.
> Currently q35 is the only machine type that supports intel-iommu.
> And we want to retain the current default behavior for q35 to avoid
> any new issues with live migration.
I guess "existing machine type" means e.g. pc-q35-2.11 and older ones,
rather than creating another machine type in parallel with q35. So we
can set 48 bits as default on upcoming pc-q35-2.12 machines, while
keep the 39 bits on the old ones.
Please refer to include/hw/compat.h.
>
> >
> > > with live migration of
> > > intel-iommu enabled QEMU guest. The only valid values for 'x-aw-bits'
> > > parameter are 39 and 48.
> >
> > I'd rather make it a boolean then.
>
> Right. It seems Intel already has additional sizes supported so keeping
> it as an integer seems better.
Yes, considering that 5-level IOMMUs are coming (AFAIK).
--
Peter Xu
Re: [Qemu-devel] [PATCH v1 0/2] intel-iommu: Extend address width to 48 bits, Peter Xu, 2017/11/15