Re: [edk2] OVMF broken under Xen (in PCI initialisation)

[Wei Liu <wei.liu2@citrix.com>]

On Thu, May 05, 2016 at 08:03:05AM +0000, Ni, Ruiyu wrote:
> Gary,
> Can you kindly teach me how to run OVMF under Xen?
> 
> I worked out a draft fix and need to verify whether
> everything is fine.
> 

Currently you need to build Xen's hvmloader, which will embed a OVMF
binary inside it.

These are some rough steps:

1. git clone xen.git from xenbits.xen.org
2. cd xen.git, create a .config file, which contains lines:
   OVMF_UPSTREAM_URL = /path/to/your/ovmf/tree
   OVMF_UPSTREAM_REVISION = $OVMF_REVISION
3. run ./configure --enable-ovmf
4. make dist -- you will get everything built in dist directory

Depending whether you have a working xen system or not, you might want
to either

1. install the xen system you just built.

or

1. get the hvmloader binary from dist/install/usr/local/lib/xen/boot
2. copy that to your working xen system

Feel free to ask questions.

As a side note, your ovmf will be cloned into tools/firmware/ directory,
you can check if xen is really building the commit you want there.

It's a bit cumbersome at the moment. Hopefully this will change in the
next release -- Anthony has a series to let you provide a firmware
binary directly.

Wei.

> Regards,
> Ray
> 
> >-----Original Message-----
> >From: Laszlo Ersek [mailto:lersek@redhat.com]
> >Sent: Thursday, April 28, 2016 6:36 PM
> >To: Ni, Ruiyu <ruiyu.ni@intel.com>; Gary Lin <glin@suse.com>
> >Cc: edk2-devel@lists.01.org <edk2-devel@ml01.01.org>; Xen Devel <xen-devel@lists.xen.org>; Kinney, Michael D
> ><michael.d.kinney@intel.com>
> >Subject: Re: [edk2] OVMF broken under Xen (in PCI initialisation)
> >
> >On 04/28/16 07:08, Ni, Ruiyu wrote:
> >
> >
> >>>>> Do you know whether Xen passes the PCI device resource
> >>>>> information to firmware?
> >>>
> >>> I don't think so, no.
> >>>
> >>> But, given that the previous PciHostBridgeDxe driver was working on Xen,
> >>> can we perhaps emulate that behavior in
> >>> "OvmfPkg/Library/PciHostBridgeLib" somehow?
> >>
> >> Let me explain the reason why previous PciHostBridgeDxe driver was
> >> working on Xen:
> >> The PciRootBridgeIo.Configuration() in new driver only create resource
> >> descriptor when the resource status is allocated:
> >>
> >> if (ResAllocNode->Status != ResAllocated) {
> >>   continue;
> >> }
> >>
> >> The same function in old driver doesn't check the Status field so it
> >> unconditionally returns BUS descriptor with AddrRangeMin and
> >> AddrRangeMax both equal 0. So that PciEnumeratorLight()
> >> in PciBus driver can still search the devices from starting bus 0.
> >> It just happened to work.
> >>
> >> I think the new driver's Configuration() implementation is correct
> >> while the old driver's one is wrong. So I don't want to change to
> >> wrong implementation to fix this issue.
> >
> >Makes sense, thank you for the explanation.
> >
> >> The issue can be resolved if we have a way to tell PciBus
> >> PciEnumeratorLight() which bus number to start searching.
> >>
> >> It's almost true that starting bus number for root bridge #0
> >> is 0. But it might not be true for the rest root bridges.
> >>
> >> OVMF's PciHostBridgeLib currently returns multiple root bridges
> >> and for root bridge #1, the starting bus number is obviously
> >> not 0 unless "etc/extra-pci-roots" doesn't exist or is 0 so there is
> >> only one root bridge.
> >>
> >> My question is in OVMF over Xen, does "etc/extra-pci-roots" exist?
> >> If it exists, device behind root bridge #1, #2... can *not* be found
> >> with the current implementation.
> >
> >"etc/extra-pci-roots" (more precisely, fw_cfg in general) is specific to
> >QEMU. QemuFwCfgLib runs alright in Xen guests, but whenever you look for
> >an fw_cfg file, it is not found -- which is good behavior.
> >
> >So, OVMF's PciHostBridgeLib produces exactly one PCI_ROOT_BRIDGE object
> >when it runs on Xen. ExtraRootBridges is set to zero, the loop runs zero
> >times, and the one InitRootBridge() call after the loop produces one
> >PCI_ROOT_BRIDGE object, with the following parameters:
> >- Bus.Base = 0
> >- Bus.Limit = PCI_MAX_BUS
> >
> >Thanks
> >Laszlo
> 
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