Re: [Xen-devel] Unable to boot Xen 4.8 with iommu=0

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/02/2017 22:47, Tamas K Lengyel wrote:
> (XEN) Switched to APIC driver x2apic_cluster.
> (XEN) XSM Framework v1.0.0 initialized
> (XEN) Flask: 128 avtab hash slots, 394 rules.
> (XEN) Flask: 128 avtab hash slots, 394 rules.
> (XEN) Flask:  5 users, 3 roles, 43 types, 2 bools
> (XEN) Flask:  12 classes, 394 rules
> (XEN) Flask:  Starting in enforcing mode.
> (XEN) xstate: size: 0x340 and states: 0x7
> (XEN) Intel machine check reporting enabled
> (XEN) Using scheduler: SMP Credit Scheduler (credit)
> (XEN) Platform timer is 14.318MHz HPET
> (XEN) Detected 3392.326 MHz processor.
> (XEN) Initing memory sharing.
> (XEN) alt table ffff82d0802d3f38 -> ffff82d0802d5564
> (XEN) PCI: MCFG configuration 0: base e0000000 segment 0000 buses 00 - 3f
> (XEN) PCI: Not using MCFG for segment 0000 bus 00-3f
> (XEN)
> (XEN) ****************************************
> (XEN) Panic on CPU 0:
> (XEN) Couldn't enable IOMMU and iommu=required/force
> (XEN) ****************************************
> (XEN)
> (XEN) Reboot in five seconds...
> (XEN) Resetting with ACPI MEMORY or I/O RESET_REG.
>
> As seen in the command line iommu is not set to required or forced.
> Yet Xen thinks it is set to required/force. Has anyone else run into
> this issue?

This area is a rats nest :(

The problem is that the APIC setup has chosen to use the x2apic_cluster
driver, which in the Xen code depends on x2APIC, which depends on
interrupt remapping, which depends on an IOMMU.

(I could have sworn we fixed this before), but the bug is that the APIC
setup shouldn't choose any of the x2apic modes if there isn't an
interrupt remapping capable IOMMU.

~Andrew

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