Re: [Xen-devel] [PATCH v5 00/16] Xen ARM DomU ACPI support

[Julien Grall <julien.grall@xxxxxxx>]

On 14/09/2016 08:32, Shannon Zhao wrote:
> 
> 
> On 2016/9/14 15:14, Julien Grall wrote:
>> Hello,
>>
>> On 14/09/2016 02:06, Stefano Stabellini wrote:
>>> On Wed, 14 Sep 2016, Shannon Zhao wrote:
>>>> On 2016/9/13 23:17, Julien Grall wrote:
>>>>>
>>>>>
>>>>> On 13/09/16 14:06, Shannon Zhao wrote:
>>>>>> Hi Julien,
>>>>>
>>>>> Hello Shannon,
>>>>>
>>>>>> On 2016/9/13 19:56, Julien Grall wrote:
>>>>>>> Hi Shannon,
>>>>>>>
>>>>>>> On 02/09/16 03:55, Shannon Zhao wrote:
>>>>>>>> From: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
>>>>>>>>
>>>>>>>> The design of this feature is described as below.
>>>>>>>> Firstly, the toolstack (libxl) generates the ACPI tables
>>>>>>>> according the
>>>>>>>> number of vcpus and gic controller.
>>>>>>>>
>>>>>>>> Then, it copies these ACPI tables to DomU non-RAM memory map
>>>>>>>> space and
>>>>>>>> passes them to UEFI firmware through the "ARM multiboot" protocol.
>>>>>>>>
>>>>>>>> At last, UEFI gets the ACPI tables through the "ARM multiboot"
>>>>>>>> protocol
>>>>>>>> and installs these tables like the usual way and passes both ACPI
>>>>>>>> and DT
>>>>>>>> information to the Xen DomU.
>>>>>>>>
>>>>>>>> Currently libxl only generates RSDP, XSDT, GTDT, MADT, FADT, DSDT
>>>>>>>> tables
>>>>>>>> since it's enough now.
>>>>>>>>
>>>>>>>> This has been tested using guest kernel with the Dom0 ACPI support
>>>>>>>> patches which could be fetched from linux master or:
>>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/mfleming/efi.git/log/?h=efi/arm-xen
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> The UEFI binary could be fetched from or built from edk2 master
>>>>>>>> branch:
>>>>>>>> http://people.linaro.org/~shannon.zhao/DomU_ACPI/XEN_EFI.fd
>>>>>>>
>>>>>>> On which commit this EFI binary is based? I am trying to rebuild
>>>>>>> myself,
>>>>>>> and go no luck to boot it so far.
>>>>>>>
>>>>>> I forgot the exact commit. But I just tried below commit which adds
>>>>>> the
>>>>>> support to edk2 and the guest can boot up successfully with ACPI.
>>>>>>
>>>>>> 402dde6 ArmVirtPkg/ArmVirtXen: Add ACPI support for Virt Xen ARM
>>>>>
>>>>> Thanks, the commit does not build on my platform. After some help for
>>>>> Ard I managed to boot UEFI with the patch [1] applied.
>>>>>
>>>>> However Linux does not boot when passing acpi=on and abort with the
>>>>> following message:
>>>>>
>>>>> (d86) 6RCU: Adjusting geometry for rcu_fanout_leaf=64, nr_cpu_ids=1
>>>>> (d86) 6NR_IRQS:64 nr_irqs:64 0
>>>>> (d86) 3No valid GICC entries exist
>>>>> (d86) 0Kernel panic - not syncing: No interrupt controller found.
>>>>> (d86) dCPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.8.0-rc6+ #420
>>>>> (d86) dHardware name: XENVM-4.8 (DT)
>>>>> (d86) Call trace:
>>>>> (d86) [<ffff000008088708>] dump_backtrace+0x0/0x1a8
>>>>> (d86) [<ffff0000080888c4>] show_stack+0x14/0x20
>>>>> (d86) [<ffff0000083d6c2c>] dump_stack+0x94/0xb8
>>>>> (d86) [<ffff00000815c24c>] panic+0x10c/0x250
>>>>> (d86) [<ffff000008c223f8>] init_IRQ+0x24/0x2c
>>>>> (d86) [<ffff000008c20a24>] start_kernel+0x238/0x394
>>>>> (d86) [<ffff000008c201bc>] __primary_switched+0x30/0x74
>>>>> (d86) 0---[ end Kernel panic - not syncing: No interrupt controller
>>>>> found.
>>>>>
>>>>> This is because the header.length for GICC is not valid for ACPI 5.1
>>>>> (see BAD_MADT_GICC_ENTRY). So please check all the size of each table
>>>>> against ACPI 5.1.
>>>>>
>>>> Oops. The reason is that acpi_madt_generic_interrupt in Xen is already
>>>> updated to ACPI 6.0 and the length is 80 not 76 of ACPI 5.1.
>>>> One solution is that we still use ACPI 5.1 and make gicc->header.length
>>>> 76. Other one is that we update to ACPI 6.0 since the Xen ARM ACPI
>>>> support in Linux was introduced after ACPI 6.0.
>>>>
>>>> Which one do you prefer?
>>>
>>> Certainly the versions of all tables need to be consistent. I would
>>> prefer to have ACPI 6.0 but 5.1 is acceptable too (especially if
>>> upgrading to 6.0 causes a large amount of changes to your patches).
>>
>> I disagree on this, we should use the first version of ACPI that is
>> fully supporting ARM because a guest operating system may choose to
>> support the first one (there is a lot hardware platform out which only
>> provides ACPI 5.1).
>>
> So you prefer we should set the gicc->header.length to 76 and still use
> ACPI 5.1, right?

That would be my preference. From my understanding, the main difference
between 6.0 and 5.1 for the MADT is a field "reserved" has been added at
the end of the GICC subtable.

However, I am wondering whether the Linux check should be relaxed.
#define BAD_MADT_GICC_ENTRY(entry, end)                                         
\
        (!(entry) || (unsigned long)(entry) + sizeof(*(entry)) > (end) ||       
\
         (entry)->header.length != ACPI_MADT_GICC_LENGTH)

But the definition of BAD_MADT_ENTRY is more relaxed as it only requires
to be greater than the size of the structure.

#define BAD_MADT_ENTRY(entry, end) (                                        \
                (!entry) || (unsigned long)entry + sizeof(*entry) > end ||  \
                ((struct acpi_subtable_header *)entry)->length < sizeof(*entry))

Any opinions?

Regards,

-- 
Julien Grall

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