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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 14 Sep 2016, 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).

And I thought that compatibility was supposed to be ACPI's strong suit.
I mistakenly had the impression that new ACPI releases weren't suppose
to break old OSes. I take back my comment, you are right that we should
stay on 5.1 (including all the erratas, many are important for ARM).

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