RE: [PATCH v3 0/2] hyperv: Run VMBus kexec cleanup from syscore shutdown

[Michael Kelley]

From: Shradha Gupta <shradhagupta@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, October 1, 2026 6:21 AM
> 
> Kexec reboot fails on ARM64 Hyper-V guests because the VMBus
> connection and SynIC CPU hotplug state are not torn down before the
> secondary CPUs are stopped. The kexec kernel consequently starts with
> the previous kernel's VMBus state still active.
> 
> The previous version added an ARM64-specific syscore shutdown
> implementation. This version follows Michael Kelley's review and moves
> the cleanup into the existing architecture-independent VMBus syscore
> operations. This removes the separate x86 handler dispatch and gives
> x86 and ARM64 the same ordering:
> 
>   device_shutdown()
>   syscore_shutdown()
>     VMBus UNLOAD and SynIC CPU hotplug teardown
>   machine_shutdown()
> 
> On x86, VMBus teardown now runs before hv_stimer_global_cleanup().
> This ordering is safe after commit be0cfab740e5 ("clocksource: hyper-v:
> Remove support for stimer interrupts in message mode") removed the
> VMBus dependency from synthetic timer handling.
> 
> Patch 1 adds a read-only helper that reports whether a kexec reboot is
> in progress. The helper is exported because HYPERV_VMBUS is tristate
> and the common syscore callback must also link when VMBus is a module.
> Patch 2 moves the cleanup into the common callback and removes the
> obsolete architecture-specific setup/remove interface.
> 
> For stable kernels that still support message-mode stimers, an
> ARM64-specific backport will be needed to preserve the existing x86
> ordering.
> 
> Changes in v3:
>   - Use the existing common VMBus syscore operations on all
>     architectures, as suggested by Michael.
>   - Remove the x86 handler pointer and the weak setup/remove interface.
>   - Add an exported read-only helper for modular VMBus builds.
>   - Correct the Fixes tag to the commit that enabled Hyper-V on ARM64.
> 
> Changes in v2:
>   - Use syscore shutdown instead of an ARM64 machine_shutdown() hook, as
>     suggested by Catalin.
> 
> Shradha Gupta (2):
>   kexec: Add helper to report an active kexec reboot
>   Drivers: hv: Run VMBus kexec cleanup from syscore shutdown
> 
>  arch/x86/kernel/cpu/mshyperv.c | 17 +----------------
>  drivers/hv/hv_common.c         | 10 ----------
>  drivers/hv/vmbus_drv.c         | 22 ++++++++++++++--------
>  include/asm-generic/mshyperv.h |  2 --
>  include/linux/kexec.h          |  2 ++
>  kernel/kexec_core.c            |  7 +++++++
>  6 files changed, 24 insertions(+), 36 deletions(-)
> 
> 
> base-commit: be0cfab740e58b70047ef6e7e3d578f00ed5d258
> --
> 2.43.0

Nice! Net impact is to remove 12 lines of code, instead of
adding 40, which is great. And nothing under arch/arm64 is
modified.

One minor point: In hv_machine_shutdown(), we have two
sequential tests of kexec_in_progress. Given that you are
removing some code under the first test, I think it would be
fair game to do a very minor refactoring of existing code and
combine the two tests. It just looks a little funny to have the
same test twice in a row.

But regardless of whether you include that change, for
the series,

Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>