On Mon, Sep 07, 2026 at 02:25:42AM -0700, Shradha Gupta wrote:
Gentle reminder.
> On ARM64, machine_shutdown() does not provide a platform hook between
> device_shutdown() and smp_shutdown_nonboot_cpus(), unlike x86's
> machine_ops.shutdown. This prevents the Hyper-V VMBus kexec handler
> from running at the correct point during kexec shutdown, causing
> kexec reboot to fail on ARM64 Hyper-V guests.
>
> Use syscore_ops.shutdown instead: syscore_shutdown() runs in the same
> window (after device_shutdown(), before CPUs are taken offline) where
> VMBus UNLOAD and cpuhp_remove_state() must execute.
>
> Provide ARM64-specific overrides of hv_setup_kexec_handler() and
> hv_remove_kexec_handler() that register/unregister a syscore_ops
> shutdown callback, replacing the __weak no-op stubs in hv_common.c.
> On x86, the existing machine_ops.shutdown mechanism is unchanged.
>
> Fixes: 9d7cf2c96758 ("Drivers: hv: Add arch independent default functions for
> some Hyper-V handlers")
> Link:
> https://lore.kernel.org/all/[email protected]/
> Suggested-by: Catalin Marinas <[email protected]>
> Signed-off-by: Shradha Gupta <[email protected]>
> Reviewed-by: Naman Jain <[email protected]>
> ---
> Changes in V2
> * Use syscore_ops.shutdown instead of a bare function pointer hook in
> machine_shutdown(), per Catalin's suggestion.
> ---
> arch/arm64/hyperv/mshyperv.c | 40 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
>
> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
> index 4fdc26ade1d7..e608e546a395 100644
> --- a/arch/arm64/hyperv/mshyperv.c
> +++ b/arch/arm64/hyperv/mshyperv.c
> @@ -15,10 +15,50 @@
> #include <linux/errno.h>
> #include <linux/version.h>
> #include <linux/cpuhotplug.h>
> +#include <linux/kexec.h>
> +#include <linux/syscore_ops.h>
> #include <asm/mshyperv.h>
>
> static bool hyperv_initialized;
>
> +/*
> + * Kexec handler registered by VMBus.
> + *
> + * On ARM64, machine_shutdown() does not provide a platform hook between
> + * device_shutdown() and smp_shutdown_nonboot_cpus(), unlike the
> + * machine_ops.shutdown mechanism used on x86. Use a syscore_ops shutdown
> + * callback instead: syscore_shutdown() runs after device_shutdown() and
> + * before CPUs are taken offline, which is the same window VMBus needs to
> + * run its UNLOAD message and cpuhp_remove_state() during kexec.
> + */
> +static void (*hv_kexec_handler_fn)(void);
> +
> +static void hv_kexec_syscore_shutdown(void *data)
> +{
> + if (kexec_in_progress && hv_kexec_handler_fn)
> + hv_kexec_handler_fn();
> +}
> +
> +static const struct syscore_ops hv_kexec_syscore_ops = {
> + .shutdown = hv_kexec_syscore_shutdown,
> +};
> +
> +static struct syscore hv_kexec_syscore = {
> + .ops = &hv_kexec_syscore_ops,
> +};
> +
> +void hv_setup_kexec_handler(void (*handler)(void))
> +{
> + hv_kexec_handler_fn = handler;
> + register_syscore(&hv_kexec_syscore);
> +}
> +
> +void hv_remove_kexec_handler(void)
> +{
> + unregister_syscore(&hv_kexec_syscore);
> + hv_kexec_handler_fn = NULL;
> +}
> +
> int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
> {
> hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION,
> --
> 2.43.0
