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

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.

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


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


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