[PATCH v4 0/2] hyperv: Run VMBus kexec cleanup from syscore shutdown

[PATCH v4 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. Move this cleanup into the VMBus syscore shutdown callback,
which runs after device shutdown and before architecture-specific machine
shutdown.

Patch 1 adds an exported helper for checking whether a normal kexec reboot
is in progress. Patch 2 runs the VMBus cleanup from the common syscore
shutdown path on x86 and ARM64, removes the old x86 handler interface, and
documents the shutdown ordering.

On x86, VMBus teardown now precedes hv_stimer_global_cleanup(). This relies
on commit be0cfab740e5 ("clocksource: hyper-v: Remove support for stimer
interrupts in message mode"). Older kernels that retain message-mode
stimer interrupts need an ARM64-specific backport to preserve the existing
x86 ordering.

Changes in v4:
  - Document the VMBus kexec cleanup path in the Hyper-V overview.
  - Combine adjacent kexec_in_progress checks in the x86 shutdown path.

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

 Documentation/virt/hyperv/overview.rst | 12 +++++++-----
 arch/x86/kernel/cpu/mshyperv.c         | 27 ++++++---------------------
 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 +++++++
 7 files changed, 36 insertions(+), 46 deletions(-)

base-commit: be0cfab740e58b70047ef6e7e3d578f00ed5d258
-- 
2.43.0

[PATCH v4 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>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Reviewed-by: Naman Jain <namjain@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 v4 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.

Document the VMBus cleanup path and its position in shutdown ordering.

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>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Reviewed-by: Naman Jain <namjain@linux.microsoft.com>
---
 Documentation/virt/hyperv/overview.rst | 12 +++++++-----
 arch/x86/kernel/cpu/mshyperv.c         | 27 ++++++---------------------
 drivers/hv/hv_common.c                 | 10 ----------
 drivers/hv/vmbus_drv.c                 | 22 ++++++++++++++--------
 include/asm-generic/mshyperv.h         |  2 --
 5 files changed, 27 insertions(+), 46 deletions(-)

diff --git a/Documentation/virt/hyperv/overview.rst b/Documentation/virt/hyperv/overview.rst
index 77408a89d1a4..34a53ba7a122 100644
--- a/Documentation/virt/hyperv/overview.rst
+++ b/Documentation/virt/hyperv/overview.rst
@@ -114,11 +114,13 @@ a shared page or remove an overlay page after the new kernel is
 using the page for a different purpose, corrupting the new kernel.
 Hyper-V does not provide a single "set everything" operation to
 guest VMs, so Linux code must individually revoke all sharing before
-doing kexec.   See hv_kexec_handler() and hv_crash_handler().  But
-the crash/panic path still has holes in cleanup because some shared
-pages are set using per-CPU synthetic registers and there's no
-mechanism to revoke the shared pages for CPUs other than the CPU
-running the panic path.
+doing kexec.  For a normal kexec reboot, the VMBus driver calls
+hv_kexec_handler() from its syscore shutdown callback, after device
+shutdown and before the architecture-specific machine shutdown.  The
+crash/panic path uses hv_crash_handler(), but still has holes in
+cleanup because some shared pages are set using per-CPU synthetic
+registers and there is no mechanism to revoke the shared pages for
+CPUs other than the CPU running the panic path.
 
 CPU Management
 --------------
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index b4af7c0a70ac..fec1c37dafbf 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;
@@ -240,17 +229,13 @@ static void hv_machine_shutdown(void)
 {
 	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.
-	 */
-	if (kexec_in_progress)
+		/*
+		 * Call hv_cpu_die() on all the CPUs, otherwise later the
+		 * hypervisor corrupts the old VP Assist Pages and can crash
+		 * the kexec kernel.
+		 */
 		cpuhp_remove_state(CPUHP_AP_HYPERV_ONLINE);
+	}
 
 	/* The function calls stop_other_cpus(). */
 	native_machine_shutdown();
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 v4 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/20261009102215.3360863-1-shradhagupta@linux.microsoft.com?part=1

Re: [PATCH v4 2/2] Drivers: hv: Run VMBus kexec cleanup from syscore shutdown

[sashiko-bot]

> 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.
> 
> Document the VMBus cleanup path and its position in shutdown ordering.
> 
> 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>

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

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261009102215.3360863-1-shradhagupta@linux.microsoft.com?part=2