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

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

[Shradha Gupta]

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

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

[Michael Kelley]

From: Shradha Gupta <shradhagupta@linux.microsoft.com> 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@outlook.com>

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

[Bradley Morgan]

On 1 October 2026 14:21:25 BST, Shradha Gupta
<shradhagupta@linux.microsoft.com> wrote:
>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
>

Wow! Great!!!

Whole series:

Reviewed-by: Bradley Morgan <brads@mainlining.org>

--- Thanks!
"I'm not a very positive person" - Linus torvalds

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

[Shradha Gupta]

On Thu, Oct 01, 2026 at 04:14:22PM +0000, Michael Kelley wrote:
> From: Shradha Gupta <shradhagupta@linux.microsoft.com> 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@outlook.com>

Thank you Michael, I'll take up the refactoring in a seperate patch.

regards,
Shradha

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

[Naman Jain]

On 10/1/2026 6:51 PM, Shradha Gupta wrote:
> 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

Since the approach changed in this version and previously reviewed-by 
tags were not applicable, sharing them again for the series.

Reviewed-by: Naman Jain <namjain@linux.microsoft.com>

Regards,
Naman