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Re: [Xen-devel] Xen 4.2 with EFI on IBM x3650 ACPI Bug


I am digging up the old thread  just to show a workaround for the
IBM xSeries ACPI problem under EFIâ

On Fri, Oct 19, 2012 at 01:33:07PM -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, Oct 19, 2012 at 09:10:36AM +0100, Jan Beulich wrote:
> > >>> On 19.10.12 at 01:43, Allan Scheid <avs.009@xxxxxxxxx> wrote:
> > > Bad news, i am seeing the log output and after the xen.efi boot this still
> > > appears on log:
> > > 
> > > Into messages:
> > > Oct 18 20:27:36 lca-fw kernel: [    0.000000] ACPI BIOS Bug: Error: A 
> > > valid
> > > RSDP was not found (20120711/tbxfroot-219)
> > > Oct 18 20:27:36 lca-fw kernel: [    0.000000] NUMA turned off
> > > Oct 18 20:27:36 lca-fw kernel: [    3.759750] pci 0000:00:01.0: can't find
> > > IRQ for PCI INT A; please try using pci=biosirq
> > > Oct 18 20:27:36 lca-fw kernel: [    3.764011] pci 0000:00:1a.0: can't find
> > > IRQ for PCI INT A; please try using pci=biosirq

IRQs are not the only problem. Only a single CPU would be detected
without ACPI.

> > Of course - you also need the kernel to be capable of obtaining
> > the necessary EFI information from Xen. That's a separate patch
> > (an early port of the one we have to the pvops kernel was
> > posted on the list a few months ago, but I don't know what its
> > status or disposition is - Konrad?).

Yeahâ it will be great to see this patch set updated and included

> Daniel is taking a stab at it. He got the hardware. But this is good
> to know that there is hardware that removes the RSDT from the low memory
> and only allows to get it from the EFI. 

The firmware rather does not copy the RSDT to the low memory before
trying to boot in the legacy BIOS mode.

And here is the workaround, which does not require kernel patching:

1. Make sure your kernel is compiled with CONFIG_KEXEC=y (kexec is not
needed for the workaround, but it enables the Linux kernel command-line
option used later)

2. Boot xen natively via EFI â use xen.efi not GRUB multiboot (GRUB
EFI chainloader will be ok too)

3. Note the RSDP address found by Xen:

# xl dmesg | grep RSDP
(XEN) ACPI: RSDP 7F7FE014, 0024 (r2 IBM   )

4. Add this to the dom0 kernel command-line (in the xen.cfg file used by


The Linux kernel will find the ACPI RSDP and will be able to initialize
IRQs and SMP properly.  This still won't be a proper EFI interface, so
the 'efivars' module and 'efibootmgr' utility won't work, but this is
not as critical as ACPI.


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