[Xen-devel] [RFC 0/8] xen/arm: acpi: Support SPIs routing

[Julien Grall <julien.grall@xxxxxxx>]

Hi all,

Currently, Xen does not route SPIs to DOM0 when ACPI is inuse after
the functionality has been reverted in Xen 4.7 by commit 909bd14.

In the previous approach, the SPIs was routed when DOM0 was writing into
ISENABLER. However, this has resulted to deadlock (see more details in [1])
as soon as the IRQ was enabled by DOM0.

We have multiple solutions to route the IRQ:
 1) Rework route_irq_to_guest to avoid the deadlock
 2) Route and enable the IRQ outside of the emulation of ISENABLER
 3) Remove the dependency on the IRQ type in the routing function
 and route all the unused IRQs during domain building
 4) Add a new hypercall to let DOM0 routing the IRQ

I think that 1) and 2) are not resilient because route_irq_to_guest may fail
and there is no way to report this error to the guest (except by killing it).

Furthermore, in solution 2) enabling the interrupt would need to be defer
until the routing has been done. This would require a lot of code duplication.

Which leave solution 3) and 4). The solution 4) requires to introduce a new
(or re-use one) stable hypercall. I am not sure why we ruled out this
solution when we reviewed the ACPI design document.

This patch series is implementing the 3rd solution which defer the IRQ
type configuration for DOM0 IRQ when ACPI is inuse. However, this will
slightly increase the memory usage of Xen (54KB).

I am happy to consider any other solutions.

I only tested briefly this patch series, Shanker can you give a try on
your hardware?

A branch with all the patches can be found here:

git://xenbits.xen.org/people/julieng/xen-unstable.git branch 
irq-routing-acpi-rfc

Yours sincerely,

[1] http://lists.xenproject.org/archives/html/xen-devel/2016-05/msg02633.html

Julien Grall (8):
  xen/arm: gic: Consolidate the IRQ affinity set in a single place
  xen/arm: gic: Do not configure affinity for guest IRQ during routing
  xen/arm: gic: split set_irq_properties
  xen/arm: gic: set_type: Pass the type in parameter rather than in
    desc->arch.type
  xen/arm: gic: Document how gic_set_irq_type should be called
  Revert "xen/arm: warn the user that we cannot route SPIs to Dom0 on
    ACPI"
  xen/arm: Allow DOM0 to set the irq type when ACPI is inuse
  xen/arm: acpi: route all unused IRQs to DOM0

 xen/arch/arm/domain_build.c | 19 ++++++++-----------
 xen/arch/arm/gic-v2.c       | 28 +++++++++++++---------------
 xen/arch/arm/gic-v3.c       | 22 ++++++++++------------
 xen/arch/arm/gic.c          | 34 ++++++++++++++++++++++------------
 xen/arch/arm/irq.c          | 14 +++++++++++++-
 xen/arch/arm/vgic.c         | 34 ++++++++++++++++++++--------------
 xen/include/asm-arm/gic.h   | 11 +++++++----
 xen/include/asm-arm/irq.h   |  6 ++++++
 8 files changed, 99 insertions(+), 69 deletions(-)

-- 
1.9.1


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