Re: [Xen-devel] [PATCH] x86-64: one more adjustment for Fam10 MMCONF enabling

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 23.11.10 at 22:37, Sander Eikelenboom <linux@xxxxxxxxxxxxxx> wrote:
> Is there anything i have to configure for the "Fam10 MMCONF" to be enabled ?
> From what i see from my "xm dmesg" it's not enabled, although it's a family 
> 10h cpu (phenom x6)
> 
> (XEN) ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 dfl dfl)
> (XEN) ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 low level)
> (XEN) ACPI: IRQ0 used by override.
> (XEN) ACPI: IRQ2 used by override.
> (XEN) ACPI: IRQ9 used by override.
> (XEN) Enabling APIC mode:  Flat.  Using 2 I/O APICs
> (XEN) ACPI: HPET id: 0x8300 base: 0xfed00000
> (XEN) PCI: MCFG configuration 0: base e0000000 segment 0 buses 0 - 255
> (XEN) PCI: Not using MMCONFIG.

Your BIOS apparently sets up MCFG (including a valid ACPI table)
but fails to reserve the range in the E820 table, which is taken as
a strong indication to not use it. For Linux, it's being debated
whether the command line override ("mmcfg=amd-fam10" in the
Xen case) should force a reserved region into the E820 table (so
that the later check succeeds). I'm intending to submit a
corresponding Xen patch if on the Linux side the decision is
taken to do so (albeit I'm not fully convinced that this is the
right thing to do, I agree to the point being made that this
would normally only be done when the command line option
was explicitly given - the exception being a DMI white listed set
of systems).

There's no other workaround I know of, since Xen (other than
Linux) doesn't have a mechanism to force an E820 reserved
region from the command line.

Jan


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