Re: [PATCH v5 08/10] x86: hyperv: Add mshv_handler irq handler and setup function

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

On Wed, Feb 26, 2025 at 03:08:02PM -0800, Nuno Das Neves wrote:
> This will handle SYNIC interrupts such as intercepts, doorbells, and
> scheduling messages intended for the mshv driver.
> 
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> Reviewed-by: Wei Liu <wei.liu@kernel.org>
> Reviewed-by: Tianyu Lan <tiala@microsoft.com>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 9 +++++++++
>  drivers/hv/hv_common.c         | 5 +++++
>  include/asm-generic/mshyperv.h | 1 +
>  3 files changed, 15 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 0116d0e96ef9..616e9a5d77b4 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -107,6 +107,7 @@ void hv_set_msr(unsigned int reg, u64 value)
>  }
>  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);
> @@ -117,6 +118,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
>  	struct pt_regs *old_regs = set_irq_regs(regs);
>  
>  	inc_irq_stat(irq_hv_callback_count);
> +	if (mshv_handler)
> +		mshv_handler();

Can mshv_handler be defined as a weak symbol doing nothing instead
of defining it a null pointer?
This should allow to simplify this code and get rid of
hv_setup_mshv_handler, which looks redundant.

Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>

> +
>  	if (vmbus_handler)
>  		vmbus_handler();
>  
> @@ -126,6 +130,11 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
>  	set_irq_regs(old_regs);
>  }
>  
> +void hv_setup_mshv_handler(void (*handler)(void))
> +{
> +	mshv_handler = handler;
> +}
> +
>  void hv_setup_vmbus_handler(void (*handler)(void))
>  {
>  	vmbus_handler = handler;
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 2763cb6d3678..f5a07fd9a03b 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -677,6 +677,11 @@ void __weak hv_remove_vmbus_handler(void)
>  }
>  EXPORT_SYMBOL_GPL(hv_remove_vmbus_handler);
>  
> +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))
>  {
>  }
> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
> index 1f46d19a16aa..a05f12e63ccd 100644
> --- a/include/asm-generic/mshyperv.h
> +++ b/include/asm-generic/mshyperv.h
> @@ -208,6 +208,7 @@ 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));
>  
>  extern int vmbus_interrupt;
>  extern int vmbus_irq;
> -- 
> 2.34.1
>