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RE: [Xen-devel] [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_

From: Durrant, Paul
Subject: RE: [Xen-devel] [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE
Date: Wed, 15 Jan 2020 08:33:02 +0000

> -----Original Message-----
> > Linux PCI subsytem has an option resource_alignment that can be
> > applied to either a single device or all devices.  Booting with
> > pci=resource_aligment=4096 will align each device to a page.  Do you
> > think pciback should force resource_alignment=4096 for dom0?

That sounds like a good idea.
> Ideally Xen should keep track of the BARs position and size and refuse
> to passthrough devices that have BARs sharing a page with other
> devices BARs.
> > Are
> > there other MMIO ranges to be concerned about adjacent to BARs?
> IIRC you can have two BARs of different devices in the same 4K page,
> BARs are only aligned to it's size, so BARs smaller than 4K are not
> required to be page aligned.

If we had a notion of assignment groups for this, as well as devices sharing 
requester id, then Xen would not need to refuse pass-through, it would just 
require that all devices sharing the page were passed through as a unit.


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