Re: [Xen-devel] PXE boot with e1000 using OVMF

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Wed, Sep 19, 2018 at 11:04:22AM -0600, Tamas K Lengyel wrote:
> On Wed, Sep 19, 2018 at 10:36 AM Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> >
> > On Wed, Sep 12, 2018 at 11:54:02AM -0600, Tamas K Lengyel wrote:
> > > HI all,
> > > I'm experimenting with OVMF and I checked to see if OVMF can do PXE
> > > boot out-of-the box with a e1000 emulated network interface and was
> > > surprised to find that it does not. After reading some of the prior
> > > discussions on the topic (https://lists.gt.net/xen/devel/382432 and
> > > https://lists.xenproject.org/archives/html/xen-users/2015-09/msg00059.html)
> > > I was able to get the menu options to show up by copying efi-e1000.rom
> > > that gets installed by Xen's QEMU build into the disk of the VM and
> > > then loading with loadpcirom manually in the EFI shell. From the prior
> > > discussions it sounds to me like this option rom should have been
> > > automatically served by QEMU to OVMF when the VM started as an
> > > OptionROM. So is this a bug or what's missing?
> >
> > Doesn't QEMU load the option ROM automatically when you specify e1000?
> >
> > I _think_ it loads option ROM automatically because I have seen complain
> > that if you configure too many emulated NICs the guest runs out of
> > memory.
> 
> I compiled QEMU with DEBUG_PCI enabled in hw/pci/pci.c and then the
> log shows efi-e1000.rom being loaded. However, AFAICT since PCI
> enumeration is disabled in OVMF when running under Xen (I'm not
> exactly sure why) the option rom never gets executed as it only gets

It's because hvmloader (which is runned before OVMF start) takes care of
enumerating the PCI bus. OVMF only has to read the information:
via OvmfPkg/Library/PciHostBridgeLib/XenSupport.c

I can try to find out what's needed in order to load an option rom, or
ask on edk2-devel.

> called from the enumeration route
> (https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Bus/Pci/PciBusDxe/PciEnumerator.h#L63).
> At least that's my current understanding of how option roms work under
> OVMF.

-- 
Anthony PERARD

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