Re: [Xen-devel] [PATCH 0/7] xen/arm: CPU hotplug fixes

[Julien Grall <julien.grall@xxxxxxx>]

Hi Mirela,

Thank you for sending the series.

On 11/04/18 14:19, Mirela Simonovic wrote:
> This patch set contains fixes required to enable CPU hotplug for secondary CPUs.
> CPU hotplug of secondary CPUs will be used for suspend to RAM support for ARM.
>
> With these patches calling disable_nonboot_cpus() from the boot CPU will cause
> all secondary CPUs to be stopped. When a CPU is stopped it will issue the PSCI
> CPU_OFF call to the EL3. The calling CPU will be powered down if the underlying
> firmware allows so. If the CPU_OFF is not supported by the underlying firmware
> the calling CPU will stay in infinite WFI loop. When secondary CPUs are stopped
> all interrupts targeted to them are migrated to the boot CPU.
> Calling enable_nonboot_cpus() from the boot CPU will cause all secondary CPUs
> to be hotplugged. When a CPU is hotplugged the interrupts' affinity is restored.
I think this patch series is not complete. While it may work for you 
there are a few corner cases that will result to leak some memory 
everytime you turn off/on the CPU. This is the case of page-table, 
action associated to local IRQ.... I don't have a full list, but 
basically you need to ensured that anything that was initialized during 
the CPU boot are freed/reverted. You probably want to look at my answer 
you on your design document [1] for more details.
I also don't see any code migrating Xen interrupt from the CPU that is 
going to be turned off to the other. Is it something you are going to 
plan for the future?
> Calls to enable/disable_nonboot_cpus() functions currently don't exist in
> Xen ARM code. This will be added with the suspend to RAM support for ARM.
What would be the way to test that series?

> The code is tested on Xilinx Zynq UltraScale+ MPSoC/ZCU102 board (includes
> physical power down/up of secondary CPUs).
>
> Mirela Simonovic (7):
>    xen/arm: Added handling of the trapped access to OSLSR register
>    xen/arm/vgic-v2: Ignore write to GICD_ISACTIVERn registers
>    xen/arm/psci: Implement CPU_OFF PSCI call (physical interface)
>    xen/arm: When CPU dies, free percpu area immediatelly
>    xen/arm: Remove __initdata and __init to enable CPU hotplug
>    xen/arm: Setup virtual paging for secondary CPUs in non-boot scenario
>    xen/arm: Restore IRQ affinity after hotplugging a CPU
>
>   xen/arch/arm/arm64/smpboot.c   |  2 +-
>   xen/arch/arm/arm64/vsysreg.c   |  3 ++-
>   xen/arch/arm/irq.c             |  2 +-
>   xen/arch/arm/p2m.c             | 10 ++++++++--
>   xen/arch/arm/percpu.c          |  2 +-
>   xen/arch/arm/processor.c       |  2 +-
>   xen/arch/arm/psci.c            |  5 +++++
>   xen/arch/arm/smpboot.c         | 14 ++++++++++++--
>   xen/arch/arm/vgic-v2.c         |  3 +--
>   xen/common/schedule.c          |  4 ++++
>   xen/include/asm-arm/p2m.h      |  3 +++
>   xen/include/asm-arm/procinfo.h |  4 ++--
>   xen/include/asm-arm/psci.h     |  1 +
>   13 files changed, 42 insertions(+), 13 deletions(-)
Cheers,

[1] See [RFC v2] xen/arm: Suspend to RAM Support in Xen for ARM

--
Julien Grall

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