Re: [Xen-devel] [PATCH for 4.5 v7 1/1] Add mmio_hole_size

[Don Slutz <dslutz@xxxxxxxxxxx>]

On 10/15/14 12:12, Wei Liu wrote:
> On Tue, Oct 14, 2014 at 11:56:22AM -0400, Konrad Rzeszutek Wilk wrote:
> > On Mon, Oct 13, 2014 at 08:51:19AM -0400, Don Slutz wrote:
> > > If you add enough PCI devices then all mmio may not fit below 4G
> > > which may not be the layout the user wanted. This allows you to
> > > increase the below 4G address space that PCI devices can use and
> > > therefore in more cases not have any mmio that is above 4G.
> > >
> > > There are real PCI cards that do not support mmio over 4G, so if you
> > > want to emulate them precisely, you may also need to increase the
> > > space below 4G for them. There are drivers for these cards that also
> > > do not work if they have their mmio space mapped above 4G.
> > >
> > > This allows growing the MMIO hole to the size needed.
> > >
> > > This may help with using pci passthru and HVM.
> > >
> > > Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
> > Wei, Ian, Stefano, Ian,
> >
> > I am OK with this patch going in Xen 4.5 (as a release-manager)
> > but it can't go anywhere unless there is an Ack/Review.
> >
> > P.S.
> > Also added Wei to the CC list.
> I didn't follow this closely. ISTR there's disagreement on whether this
> is the correct approach to fix this bug. Have we reached consent that we
> should use this approach?
I was hoping that if someone did have a disagreement with this
approach, they would have responded to this e-mail.  As far as I
know the only disagreement is on bug #28:


 #28 - support PCI hole resize in qemu-xen

http://bugs.xenproject.org/xen/bug/28

since this approach is not supporting PCI hole resize in qemu-xen.

> From Jan Beulich:
> > From Don Slutz:
> > The support for changing mmio_hole_size is still "missing" from QEMU.
> > So this code only works for qemu-traditional.  I think Jan said
> > back on v1 or v2 (sorry, e-mail issues) that since this is a config,
> > disable the auto changing code.
> Because it didn't seem like you would want to properly take care
> of both cases together (iirc the fact that the configured hole size
> could be other than a power of 2 introduced a conflict with the
> current resizing logic). I.e. doing one or the other is a suitable
> first step imo, but with room for improvement.

So I am going with this 1st step and not claiming to fix bug #28.

   -Don Slutz


> Wei.

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