Re: [Xen-devel] ACPI-Tables corrupted?

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

Strictly speaking we should have a stab at disabling x2apic as well, but
that's harder. And not necessary for newer Linux kernels, which is what we
will usually be kexec'ing to anyway.

 -- Keir

On 29/07/2010 07:40, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

> It's not a dom0, it's a kexec'ed crash kernel. We should be reinstating DMAR
> before jumping into a native kernel. I will sort out a fix.
> 
>  -- Keir
> 
> On 29/07/2010 07:31, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
> 
>> A bit curios, why enable_IR_x2apic() will be called in dom0? IMO, dom0 will
>> not control interrupt controller, either xapic, or x2apic. Shouldn't this be
>> commented out in pvops dom0?
>> 
>> What's the panic point in your environment? Is it the following code? If yes,
>> that means you enable x2apic in BIOS and you can workaround this issue by
>> disable x2apic in BIOS.
>> 
>>         if (x2apic_preenabled)
>>                  panic("x2apic: enabled by BIOS but kernel init failed.");
>> 
>> Thanks
>> --jyh
>> 
>>> -----Original Message-----
>>> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>>> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Juergen Gross
>>> Sent: Wednesday, July 28, 2010 8:14 PM
>>> To: Keir Fraser
>>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>>> Subject: Re: [Xen-devel] ACPI-Tables corrupted?
>>> 
>>> On 07/28/2010 01:39 PM, Keir Fraser wrote:
>>>> 
>>>> 
>>>> 
>>>> On 28/07/2010 12:26, "Juergen Gross"<juergen.gross@xxxxxxxxxxxxxx>  wrote:
>>>> 
>>>>> On 07/28/2010 12:03 PM, Keir Fraser wrote:
>>>>>> On 28/07/2010 10:38, "Juergen Gross"<juergen.gross@xxxxxxxxxxxxxx>
>>> wrote:
>>>>>> 
>>>>>>> As you can see, the DMAR eye-catcher is replaced by blanks!
>>>>>>> This leads to a programmed panic in the crash kernel later in case of a
>>>>>>> panic in dom0...
>>>>>>> 
>>>>>>> Any ideas?
>>>>>>> BTW: seen in unstable AND 4.0
>>>>>> 
>>>>>> Look at the tail of xen/drivers/passthrough/vtd/dmar.c: Xen *always*
>>>>>> *unconditionally* trashes the DMAR so that dom0 will not parse it.
>>>>>> Presumably bad stuff would happen if it did.
>>>>> 
>>>>> As Dom0 is a pv-kernel, it should be able to ignore this entry.
>>>>> The crash kernel OTOH should not panic due to the trashed entry!
>>>>> What is the correct solution here?
>>>> 
>>>> Could provide a cmdline option to not nobble the DMAR?
>>> 
>>> That's a possibility.
>>> I wonder whether it wouldn't be better to let dom0 decide not to use it if
>>> running under xen. This would remove the requirement for zapping the ACPI
>>> table. IMO it's always a bad idea to change data of a deeper layer...
>>> 
>>>> 
>>>>> The crash kernel expects a valid DMAR entry, as following code in
>>>>> enable_IR_x2apic() suggests:
>>>> 
>>>> I don't know what that function does, nor how the error path below depends
>>>> on DMAR. DMAR isn't mentioned in the below code.
>>> 
>>> Sorry, here a larger fragment (source arch/x86/kernel/apic/apic.c):
>>> 
>>> void __init enable_IR_x2apic(void)
>>> {
>>>         unsigned long flags;
>>>         struct IO_APIC_route_entry **ioapic_entries = NULL;
>>>         int ret, x2apic_enabled = 0;
>>>         int dmar_table_init_ret = 0;
>>> 
>>> #ifdef CONFIG_INTR_REMAP
>>>         dmar_table_init_ret = dmar_table_init();
>>>         if (dmar_table_init_ret)
>>>                 pr_debug("dmar_table_init() failed with %d:\n",
>>>                                 dmar_table_init_ret);
>>> #endif
>>> 
>>>         ioapic_entries = alloc_ioapic_entries();
>>>         if (!ioapic_entries) {
>>>                 pr_err("Allocate ioapic_entries failed\n");
>>>                 goto out;
>>>         }
>>> 
>>>         ret = save_IO_APIC_setup(ioapic_entries);
>>>         if (ret) {
>>>                 pr_info("Saving IO-APIC state failed: %d\n", ret);
>>>                 goto out;
>>>         }
>>> 
>>>         local_irq_save(flags);
>>>         mask_8259A();
>>>         mask_IO_APIC_setup(ioapic_entries);
>>> 
>>>         if (dmar_table_init_ret)
>>>                 ret = 0;
>>>         else
>>>                 ret = enable_IR();
>>> 
>>>         if (!ret) {
>>>                 /* IR is required if there is APIC ID > 255 even when
>>> running
>>>                  * under KVM
>>>                  */
>>>                 if (max_physical_apicid > 255 || !kvm_para_available())
>>>                         goto nox2apic;
>>>                 /*
>>>                  * without IR all CPUs can be addressed by IOAPIC/MSI
>>>                  * only in physical mode
>>>                  */
>>>                 x2apic_force_phys();
>>>         }
>>> 
>>>         x2apic_enabled = 1;
>>> 
>>>         if (x2apic_supported() && !x2apic_mode) {
>>>                 x2apic_mode = 1;
>>>                 enable_x2apic();
>>>                 pr_info("Enabled x2apic\n");
>>>         }
>>> 
>>> nox2apic:
>>>         if (!ret) /* IR enabling failed */
>>>                 restore_IO_APIC_setup(ioapic_entries);
>>>         unmask_8259A();
>>>         local_irq_restore(flags);
>>> 
>>> out:
>>>         if (ioapic_entries)
>>>                 free_ioapic_entries(ioapic_entries);
>>> 
>>>         if (x2apic_enabled)
>>>                 return;
>>> 
>>>         if (x2apic_preenabled)
>>>                 panic("x2apic: enabled by BIOS but kernel init failed.");
>>>         else if (cpu_has_x2apic)
>>>                 pr_info("Not enabling x2apic, Intr-remapping init
>>> failed.\n");
>>> }
>>> 
>>> 
>>> dmar_table_init() will return -ENODEV if no DMAR record is found.
>>> 
>>> 
>>> Juergen
>>> 
>>> --
>>> Juergen Gross                 Principal Developer Operating Systems
>>> TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
>>> Fujitsu Technology Solutions              e-mail:
>>> juergen.gross@xxxxxxxxxxxxxx
>>> Domagkstr. 28                           Internet: ts.fujitsu.com
>>> D-80807 Muenchen                 Company details:
>>> ts.fujitsu.com/imprint.html
>>> 
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>>> http://lists.xensource.com/xen-devel
> 
> 
> 
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