[PATCH 0/5] Improve PSCI system events and fix reboot bugs

[Andrew Jones]

On Thu, Nov 27, 2014 at 07:40:55PM +0100, Christoffer Dall wrote:
> Several people have reported problems with rebooting ARM VMs, especially
> on 32-bit ARM.  This is mainly due to the same reason we were seeing
> boot errors in the past, namely that the ram, dcache, and icache weren't
> coherent on guest boot with the guest (stage-1) MMU disabled.  We solved
> this by ensuring coherency when we fault in pages, but since most memory
> is already mapped after a reboot, we don't do anything.
> 
> The solution is to unmap the regular RAM on system events, but we must
> take care to not unmap the GIC or other IO regions, hence the somehwat
> complicated solution.
> 
> As part of figuring this out, it became clear that some semantics around
> the KVM_ARM_VCPU_INIT ABI and system event ABI was unclear (what is
> userspace expected to do when it receives a system event).  This series
> also clarifies the ABI and changes the kernel functionality to do what
> userspace expects (turn off VCPUs on a system shutdown event).
> 
> The code is avaliable here as well:
> http://git.linaro.org/people/christoffer.dall/linux-kvm-arm.git vcpu_init_fixes
> 
> There is an alternative version with more code reuse for what is patch 4
> in this series available here:
> http://git.linaro.org/people/christoffer.dall/linux-kvm-arm.git vcpu_init_fixes-alternative
> 
> See patch 4 for more info on this one.
> 
> Testing
> -------
> This has been tested on CubieBoard, Arndale, TC2, and Juno.  On Arndale
> and TC2 it was extremely easy to reproduce the setup (just start a VM
> that runs reboot from /etc/rc.local or similar) and this series clearly
> fixes the behavior.

We've also seen reboots leading to a stuck vcpu. It appeared to be 100%
reproducible on a freshly installed guest (first reboot after running
the installer), and then intermittently afterwards. I've just tested
this patch series, and it appears to resolve the issue. No stuck vcpu
after install, and a reboot loop has been running for a while now. I'm
testing on a mustang. If you like, feel free to add a

Tested-by: Andrew Jones <drjones at redhat.com>

drew

> 
> On Juno we occasionally see lockups of reboot, but I see this both with
> and without this series.  I have run a VM in a loop where the guest
> shuts itself down (same code path) a couple of hundred times without
> seeing any issues, so I think it's safe to merge this and further
> investigate the Juno reboot issue.
> 
> 
> Christoffer Dall (5):
>   arm/arm64: KVM: Correct KVM_ARM_VCPU_INIT power off option
>   arm/arm64: KVM: Reset the HCR on each vcpu when resetting the vcpu
>   arm/arm64: KVM: Clarify KVM_ARM_VCPU_INIT ABI
>   arm/arm64: KVM: Introduce stage2_unmap_vm
>   arm/arm64: KVM: Turn off vcpus and flush stage-2 pgtables on sytem
>     exit events
> 
>  Documentation/virtual/kvm/api.txt    | 10 +++++-
>  arch/arm/include/asm/kvm_emulate.h   |  5 +++
>  arch/arm/include/asm/kvm_mmu.h       |  1 +
>  arch/arm/kvm/arm.c                   |  4 +++
>  arch/arm/kvm/guest.c                 |  1 -
>  arch/arm/kvm/mmu.c                   | 65 ++++++++++++++++++++++++++++++++++++
>  arch/arm/kvm/psci.c                  | 18 ++++++++++
>  arch/arm64/include/asm/kvm_emulate.h |  5 +++
>  arch/arm64/include/asm/kvm_host.h    |  1 +
>  arch/arm64/include/asm/kvm_mmu.h     |  1 +
>  arch/arm64/kvm/guest.c               |  1 -
>  11 files changed, 109 insertions(+), 3 deletions(-)
> 
> -- 
> 2.1.2.330.g565301e.dirty
> 
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