Re: [Xen-devel] [PATCH RESEND 1/3] OvmfPkg/XenSupport: remove usage of prefetchable PCI host bridge aperture

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Mar 06, 2019 at 12:40:54PM +0000, Igor Druzhinin wrote:
> This aperture doesn't exist in OVMF and trying to use it causes
> failing assertions later in cases there are prefetchable and
> non-prefetchable BARs following each other. This configuration is
> quite likely with some PCI passthrough devices.

According to the PCIe spec, it's fine to place prefetchable BARs in
non-prefetchable memory space. There's a note that says that most
implementations will only have 1G of non-prefetchable memory, and
that most scalable platforms will map 32bit BARs into
non-prefetchable memory regardless of the prefetchable bit value.

Shouldn't OVMF be fine with finding both prefetchable and
non-prefetchable BARs, as long as the memory region is set to
non-prefetchable?

Does OVMF have the capability to position BARs by itself? If so we
could skip of the placement done by hvmloader and just let OVMF
position things where it see fit.

Thanks, Roger.

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