On 2015/8/4 22:37, Stefano Stabellini wrote:
On Tue, 4 Aug 2015, Shannon Zhao wrote:
This document is going to explain the design details of Xen booting with
ACPI on ARM. Maybe parts of it may not be appropriate. Any comments are
welcome.
Good start!
To Xen itself booting with ACPI, this is similar to Linux kernel except
that Xen doesn't parse DSDT table. So I'll skip this part and focus on
how Xen prepares ACPI tables for DOM0 and how Xen passes them to DOM0.
1)copy and change some EFI and ACPI tables.
a) Copy EFI_SYSTEM_TABLE and change the value of FirmwareVendor,
VendorGuid, VendorTable, ConfigurationTable. These changes are not
very special and it just assign values to these members.
b) Create EFI_MEMORY_DESCRIPTOR table. This will add memory start and
size information of DOM0. And DOM0 will get the memory information
through this EFI table.
c) Copy FADT table. Change the value of arm_boot_flags to enable PSCI
and HVC. Let the hypervisor_id be "XenVMM" in order to tell DOM0
that it runs on Xen hypervisor, so DOM0 can call hypercall to get
some informations for booting necessity, such as grant tab start
address and size. Change header revison, length and checksum as
well.
d) Copy GTDT table. Set non_secure_el2_interrupt and
non_secure_el2_flags to 0 to mask EL2 timer for DOM0.
e) Copy MADT table. According to the value of dom0_max_vcpus to change
the number GICC entries.
f) Create STAO table. This table is a new added one that's used to
define a list of ACPI namespace names that are to be ignored by the
OSPM in DOM0. Currently we use it to tell OSPM should ignore UART
defined in SPCR table.
g) Copy XSDT table. Add a new table entry for STAO and change other
table's entries.
h) Change the value of xsdt_physical_address in RSDP table.
i) The reset of tables are not copied or changed. They are reused
including DSDT, SPCR.
OK so far
All these tables will be copied or mapped to guest memory.
Are they copied or mapped? Also I think we need to recalculate the
md5sum?
The above changed tables are copied to DOM0 and the reused tables(DSDT,
SPCR, RSDP) are mapped to DOM0.
Yes, we need to recalculate the checksum.
2)Create minimal DT to pass required informations to DOM0
The minimal DT mainly passes DOM0 bootargs, address and size of initrd
(if available), address and size of uefi system table, address and
size of uefi memory table, uefi-mmap-desc-size and uefi-mmap-desc-ver.
I think we need to specify which Linux entry point is called, that I
think will be the proper non-EFI kernel entry point, which requires MMU
off (see Documentation/efi-stub.txt in linux).
Also it would be better to write the full bindings of the generated
minimal DT, see http://marc.info/?l=linux-kernel&m=142362266626403&w=2
and Documentation/arm/uefi.txt in linux.
Ok, will add the example of the minimal DT.
3)DOM0 how to get grant table and event channel irq informations
As said above, we assign the hypervisor_id be "XenVMM" to tell DOM0
that it runs on Xen hypervisor.
Then save the start address and size
of grant table in domain->grant_table->start_addr and
domain->grant_table->size. DOM0 can call a new hypercall
GNTTABOP_get_start_addr to get these info.
Same to event channel, we've already save interrupt number in
d->arch.evtchn_irq, so DOM0 can call a new hypercall EVTCHNOP_get_irq
to get the irq.
It would be nice to go down into more details and write the parameters
of the hypercalls in the doc as they will become a newly supported ABI.
OK, will add these informations.
The evtchnop would need to be called something like
EVTCHNOP_get_notification_irq and would need to be ARM specific (on x86
things are different).
4)How to map MMIO regions
a)Current implementation is mapping MMIO regions in Dom0 on demand
when trapping in Xen with a data abort.
I think this approach is prone to failures. A driver could program a
device for DMA involving regions not yet mapped. As a consequence the
DMA operation would fail because the SMMU would stop the transaction.
b)Another way is to map all the non-ram memory regions before booting.
But as suggested by Stefano, this will use a lot of memory to store
the pagetables.
c)Another suggested way is to use a hypercall from DOM0 to request
MMIO regions mappings after Linux complete parsing the DSDT. But I
didn't find a proper place to issue this call. Anyone has some
suggestion?
I suggested to exploit the bus_notifier callbacks and issue an hypercall
there. In the case of the PCI bus, we are already handling notifications
in drivers/xen/pci.c:xen_pci_notifier.
Once you have a struct pci_dev pointer in your hand, you can get the
MMIO regions from pdev->resource[bar].
Does that work?
I'm not sure. I just have a glance at it, not look into it deeply. Will
have a look tomorrow.
5)How route device interrupt to DOM0
Currently we route all the SPI interrupts to DOM0 before DOM0 booting.
But this maybe a workaround. What's the right choice? After DOM0
parses the interrupt information from DSDT and call a hypercall to
route them?
I think that is OK for now, but it is good for you to bring up this
point here. Dom0 will ask Xen to remap interrupts for any devices
assigned to DomU created after Dom0.
--
Shannon
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