[PATCH v10 3/4] powerpc/powernv: Override pcibios_default_alignment() to force PCI devices to be page aligned

[Bjorn Helgaas]

On Fri, Apr 14, 2017 at 4:52 PM, Benjamin Herrenschmidt
<benh at kernel.crashing.org> wrote:
> On Fri, 2017-04-14 at 10:58 -0500, Bjorn Helgaas wrote:
>> On Mon, Apr 10, 2017 at 07:58:13PM +0800, Yongji Xie wrote:
>> > This overrides pcibios_default_alignment() to set default alignment
>> > to PAGE_SIZE for all PCI devices on PowerNV platform. Thus sub-page
>> > BARs would not share a page and could be mapped into guest when
>> > VFIO
>> > passthrough them.
>>
>> Thanks for doing this.  This looks like a reasonable strategy to me,
>> but it would be good to get a powerpc ack for it.
>
> I agree in principle. I'm surprised that PowerPC is the only one
> interested here though, what about other platforms who want to use
> KVM and PCI pass-through and use Linux to assign BARs ?

If I understand correctly, the problem is with BARs smaller than a
page, and this happens more on PowerPC because larger page sizes are
more common there.

Bjorn