From: David Woodhouse <dwmw@amazon.co.uk>

If we want to do parallel CPU bringup, we're going to need to set this up
and leave it until all CPUs are done. Might as well use the RTC spinlock
to protect the refcount, as we need to take it anyway.

[Usama Arif: fixed rebase conflict]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Usama Arif <usama.arif@bytedance.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 arch/x86/kernel/smpboot.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 55cad72715d9..a19eddcdccc2 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -121,17 +121,22 @@ int arch_update_cpu_topology(void)
 	return retval;
 }
 
+
+static unsigned int smpboot_warm_reset_vector_count;
+
 static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 {
 	unsigned long flags;
 
 	spin_lock_irqsave(&rtc_lock, flags);
-	CMOS_WRITE(0xa, 0xf);
+	if (!smpboot_warm_reset_vector_count++) {
+		CMOS_WRITE(0xa, 0xf);
+		*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
+			start_eip >> 4;
+		*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
+			start_eip & 0xf;
+	}
 	spin_unlock_irqrestore(&rtc_lock, flags);
-	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
-							start_eip >> 4;
-	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
-							start_eip & 0xf;
 }
 
 static inline void smpboot_restore_warm_reset_vector(void)
@@ -143,10 +148,12 @@ static inline void smpboot_restore_warm_reset_vector(void)
 	 * to default values.
 	 */
 	spin_lock_irqsave(&rtc_lock, flags);
-	CMOS_WRITE(0, 0xf);
+	if (!--smpboot_warm_reset_vector_count) {
+		CMOS_WRITE(0, 0xf);
+		*((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
+	}
 	spin_unlock_irqrestore(&rtc_lock, flags);
 
-	*((volatile u32 *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) = 0;
 }
 
 /*
-- 
2.25.1

On Thu, Feb 02 2023 at 21:56, Usama Arif wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
>
> If we want to do parallel CPU bringup, we're going to need to set this up
> and leave it until all CPUs are done. Might as well use the RTC spinlock
> to protect the refcount, as we need to take it anyway.

https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#changelog

Aside of the 'We' this does not explain anything at all.

> [Usama Arif: fixed rebase conflict]
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> Signed-off-by: Usama Arif <usama.arif@bytedance.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This SOB chain is even more broken...

> ---
>  arch/x86/kernel/smpboot.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 55cad72715d9..a19eddcdccc2 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -121,17 +121,22 @@ int arch_update_cpu_topology(void)
>  	return retval;
>  }
>  
> +
> +static unsigned int smpboot_warm_reset_vector_count;
> +
>  static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
>  {
>  	unsigned long flags;
>  
>  	spin_lock_irqsave(&rtc_lock, flags);
> -	CMOS_WRITE(0xa, 0xf);
> +	if (!smpboot_warm_reset_vector_count++) {
> +		CMOS_WRITE(0xa, 0xf);
> +		*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
> +			start_eip >> 4;
> +		*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
> +			start_eip & 0xf;

Again: 80 characters are history. Please fix that all over the series.

Thanks,

        tglx