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

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Wed, Feb 15, 2017 at 12:30 PM, Tamas K Lengyel
<tamas.k.lengyel@xxxxxxxxx> wrote:
> On Wed, Feb 15, 2017 at 3:03 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>>> On 15.02.17 at 00:21, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> 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.
>>
>> And from going over the code I can't see how this would happen,
>> so Tamas, it would be nice if you could add some verbosity to the
>> functions involved. In particular x2apic_bsp_setup() must be
>> getting success (zero) from iommu_enable_x2apic_IR(), yet that
>> function calls iommu_supports_eim(), which ought to produce
>> false through its very first exit path in your case.
>>
>> Or wait - do you have the same issue if you use
>> "iommu=no,no-intremap"? In which case the problem would be
>> that "iommu=no" should clear more than just "iommu_enable", or
>> code checking iommu_intremap early (before iommu_setup()
>> manages to clear it in the case here) would need to made look at
>> both variables. Oddly enough acpi_parse_dmar() only bails if
>> both variables are clear, which suggests to me that
>> iommu_enable is intended to have two different meanings in
>> different contexts (master flag vs. controlling just DMA
>> remapping). Kevin, Feng - any thoughts here?
>
> iommu=no,no-intremap boots fine with "(XEN) Using APIC driver default"

And just to clarify, x2apic is disabled in this case "(XEN) Not
enabling x2APIC: depends on iommu_supports_eim."

Tamas

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