[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

[PATCH v3 1/2] kexec: Add helper to report an active kexec reboot

[Shradha Gupta]

A shutdown callback in a loadable module may need to distinguish a
kexec reboot from a normal restart, halt, or poweroff. The Hyper-V
VMBus driver needs this distinction when moving its kexec cleanup into
a common syscore shutdown callback.

Add kexec_is_in_progress() and export it to GPL modules so the callback
can remain guarded when VMBus is built as a module. Provide a false
inline implementation when CONFIG_KEXEC_CORE is disabled.

The helper reports only the normal kexec reboot path. Crash kexec and
preserve-context kexec do not set this state.

Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
---
 include/linux/kexec.h | 2 ++
 kernel/kexec_core.c   | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 8a22bc9b8c6c..827a5311d97a 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -468,6 +468,7 @@ bool kexec_load_permitted(int kexec_image_type);
 
 /* flag to track if kexec reboot is in progress */
 extern bool kexec_in_progress;
+bool kexec_is_in_progress(void);
 
 #ifndef page_to_boot_pfn
 static inline unsigned long page_to_boot_pfn(struct page *page)
@@ -544,6 +545,7 @@ static inline void *kimage_map_segment(struct kimage *image, int idx)
 { return NULL; }
 static inline void kimage_unmap_segment(void *buffer) { }
 #define kexec_in_progress false
+static inline bool kexec_is_in_progress(void) { return false; }
 #endif /* CONFIG_KEXEC_CORE */
 
 #ifdef CONFIG_KEXEC_SIG
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index dc770b9a6d05..282c7b3c6c35 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -23,6 +23,7 @@
 #include <linux/hardirq.h>
 #include <linux/elf.h>
 #include <linux/elfcore.h>
+#include <linux/export.h>
 #include <linux/utsname.h>
 #include <linux/numa.h>
 #include <linux/suspend.h>
@@ -54,6 +55,12 @@ atomic_t __kexec_lock = ATOMIC_INIT(0);
 /* Flag to indicate we are going to kexec a new kernel */
 bool kexec_in_progress = false;
 
+bool kexec_is_in_progress(void)
+{
+	return kexec_in_progress;
+}
+EXPORT_SYMBOL_GPL(kexec_is_in_progress);
+
 bool kexec_file_dbg_print;
 
 /*
-- 
2.43.0

[PATCH v3 2/2] Drivers: hv: Run VMBus kexec cleanup from syscore shutdown

[Shradha Gupta]

ARM64 Hyper-V guests do not run the VMBus kexec cleanup before
secondary CPUs are stopped. Consequently, the old VMBus connection
and SynIC state remain active when the kexec kernel starts.

Run the VMBus kexec handler from the existing VMBus syscore shutdown
callback. syscore_shutdown() runs after device shutdown and before
machine shutdown, while all CPUs needed by the SynIC CPU hotplug
teardown are still available. Guard the callback with
kexec_is_in_progress() so normal restart, halt, and poweroff paths are
unchanged.

Use the same path on x86 and remove the architecture-specific handler
pointer and the weak setup/remove interfaces. VMBus teardown now
precedes hv_stimer_global_cleanup() on x86.

The new x86 ordering relies on commit be0cfab740e5 ("clocksource:
hyper-v: Remove support for stimer interrupts in message mode"), which
removed the synthetic timer's dependency on VMBus message delivery.
Older kernels that retain message-mode stimer interrupts must preserve
the existing x86 ordering and therefore require an ARM64-specific
backport.

Fixes: 9bbb888824e3 ("arm64: hyperv: Initialize hypervisor on boot")
Link: https://lore.kernel.org/all/20260814093133.3191250-1-shradhagupta@linux.microsoft.com/
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Suggested-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
---
 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 --
 4 files changed, 15 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index b4af7c0a70ac..263f7e7acac0 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -148,7 +148,6 @@ EXPORT_SYMBOL_GPL(hv_set_msr);
 static void (*mshv_handler)(void);
 static void (*vmbus_handler)(void);
 static void (*hv_stimer0_handler)(void);
-static void (*hv_kexec_handler)(void);
 static void (*hv_crash_handler)(struct pt_regs *regs);
 
 DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
@@ -215,16 +214,6 @@ void hv_remove_stimer0_handler(void)
 	hv_stimer0_handler = NULL;
 }
 
-void hv_setup_kexec_handler(void (*handler)(void))
-{
-	hv_kexec_handler = handler;
-}
-
-void hv_remove_kexec_handler(void)
-{
-	hv_kexec_handler = NULL;
-}
-
 void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs))
 {
 	hv_crash_handler = handler;
@@ -238,13 +227,9 @@ void hv_remove_crash_handler(void)
 #ifdef CONFIG_KEXEC_CORE
 static void hv_machine_shutdown(void)
 {
-	if (kexec_in_progress) {
+	if (kexec_in_progress)
 		hv_stimer_global_cleanup();
 
-		if (hv_kexec_handler)
-			hv_kexec_handler();
-	}
-
 	/*
 	 * Call hv_cpu_die() on all the CPUs, otherwise later the hypervisor
 	 * corrupts the old VP Assist Pages and can crash the kexec kernel.
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index 31256cb22b39..bb290a5eaf1d 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -681,16 +681,6 @@ void __weak hv_setup_mshv_handler(void (*handler)(void))
 }
 EXPORT_SYMBOL_GPL(hv_setup_mshv_handler);
 
-void __weak hv_setup_kexec_handler(void (*handler)(void))
-{
-}
-EXPORT_SYMBOL_GPL(hv_setup_kexec_handler);
-
-void __weak hv_remove_kexec_handler(void)
-{
-}
-EXPORT_SYMBOL_GPL(hv_remove_kexec_handler);
-
 void __weak hv_setup_crash_handler(void (*handler)(struct pt_regs *regs))
 {
 }
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 5ebdbe24b5a1..3532ea779d34 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -33,6 +33,7 @@
 #include <linux/sysfb.h>
 #include <linux/efi.h>
 #include <linux/kernel.h>
+#include <linux/kexec.h>
 #include <linux/syscore_ops.h>
 #include <linux/dma-map-ops.h>
 #include <linux/pci.h>
@@ -2904,6 +2905,12 @@ static void hv_kexec_handler(void)
 	cpuhp_remove_state(hyperv_cpuhp_online);
 };
 
+static void hv_vmbus_syscore_shutdown(void *data)
+{
+	if (kexec_is_in_progress())
+		hv_kexec_handler();
+}
+
 static void hv_crash_handler(struct pt_regs *regs)
 {
 	int cpu;
@@ -2958,14 +2965,15 @@ static void hv_synic_resume(void *data)
 	 */
 }
 
-/* The callbacks run only on CPU0, with irqs_disabled. */
-static const struct syscore_ops hv_synic_syscore_ops = {
+/* The suspend and resume callbacks run only on CPU0, with irqs_disabled. */
+static const struct syscore_ops hv_vmbus_syscore_ops = {
 	.suspend = hv_synic_suspend,
 	.resume = hv_synic_resume,
+	.shutdown = hv_vmbus_syscore_shutdown,
 };
 
-static struct syscore hv_synic_syscore = {
-	.ops = &hv_synic_syscore_ops,
+static struct syscore hv_vmbus_syscore = {
+	.ops = &hv_vmbus_syscore_ops,
 };
 
 static int __init hv_acpi_init(void)
@@ -3014,10 +3022,9 @@ static int __init hv_acpi_init(void)
 	if (ret)
 		goto cleanup;
 
-	hv_setup_kexec_handler(hv_kexec_handler);
 	hv_setup_crash_handler(hv_crash_handler);
 
-	register_syscore(&hv_synic_syscore);
+	register_syscore(&hv_vmbus_syscore);
 
 	return 0;
 
@@ -3039,9 +3046,8 @@ static void __exit vmbus_exit(void)
 		 */
 		return;
 
-	unregister_syscore(&hv_synic_syscore);
+	unregister_syscore(&hv_vmbus_syscore);
 
-	hv_remove_kexec_handler();
 	hv_remove_crash_handler();
 	vmbus_connection.conn_state = DISCONNECTED;
 	hv_stimer_global_cleanup();
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index bf601d67cecb..98fe5c0f54ea 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -183,8 +183,6 @@ void hv_remove_vmbus_handler(void);
 void hv_setup_stimer0_handler(void (*handler)(void));
 void hv_remove_stimer0_handler(void);
 
-void hv_setup_kexec_handler(void (*handler)(void));
-void hv_remove_kexec_handler(void);
 void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs));
 void hv_remove_crash_handler(void);
 void hv_setup_mshv_handler(void (*handler)(void));
-- 
2.43.0

Re: [PATCH v3 1/2] kexec: Add helper to report an active kexec reboot

[sashiko-bot]

> A shutdown callback in a loadable module may need to distinguish a
> kexec reboot from a normal restart, halt, or poweroff. The Hyper-V
> VMBus driver needs this distinction when moving its kexec cleanup into
> a common syscore shutdown callback.
> 
> Add kexec_is_in_progress() and export it to GPL modules so the callback
> can remain guarded when VMBus is built as a module. Provide a false
> inline implementation when CONFIG_KEXEC_CORE is disabled.
> 
> The helper reports only the normal kexec reboot path. Crash kexec and
> preserve-context kexec do not set this state.
> 
> Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261001132128.1703511-1-shradhagupta@linux.microsoft.com?part=1

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