Re: [RFC] x86: Remove CALL_FUNCTION_VECTOR

["Jürgen Groß" <jgross@suse.com>]

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On 28.10.26 11:09, Peter Zijlstra wrote:
> On Tue, Jul 28, 2026 at 11:13:55AM +0530, Bharata B Rao wrote:
> 
>> diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
>> index 85253fc8e384..575f880cb147 100644
>> --- a/arch/x86/include/asm/irq_vectors.h
>> +++ b/arch/x86/include/asm/irq_vectors.h
>> @@ -105,10 +105,12 @@
>>    */
>>   #define POSTED_MSI_NOTIFICATION_VECTOR	0xeb
>>   
>> +#define IBS_MEMPROF_VECTOR		0xea
>> +
>>   #define NR_VECTORS			 256
>>   
>>   #ifdef CONFIG_X86_LOCAL_APIC
>> -#define FIRST_SYSTEM_VECTOR		POSTED_MSI_NOTIFICATION_VECTOR
>> +#define FIRST_SYSTEM_VECTOR		IBS_MEMPROF_VECTOR
>>   #else
>>   #define FIRST_SYSTEM_VECTOR		NR_VECTORS
>>   #endif
> 
> Right, so while looking at this, I noticed a few things; and I think we
> can do the below.
> 
> ---
> Subject: x86: Remove CALL_FUNCTION_VECTOR
> 
> Per the lines in linux/smp.h:
> 
>    #define generic_smp_call_function_interrupt \
> 	  generic_smp_call_function_single_interrupt
> 
> The CALL_FUNCTION_VECTOR and CALL_FUNCTION_SINGLE_VECTOR have the exact
> same handler and are thus identical.
> 
> Boot tested with vng; Xen parts completely untested.
> 
> Not-Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

The Xen parts look fine.


Juergen

> ---
> Note: we could also move HYPERV_*_VECTOR to the bottom and compress
> FIRST_SYSTEM_VECTOR depending on CONFIG_HYPERV, giving 2 interrupts back
> to !HYPERV peeps.
> 
>   arch/x86/entry/entry_fred.c        |  1 -
>   arch/x86/include/asm/idtentry.h    |  1 -
>   arch/x86/include/asm/irq_vectors.h | 39 +++++++++++++++++++-------------------
>   arch/x86/include/asm/xen/events.h  |  1 -
>   arch/x86/kernel/apic/ipi.c         |  6 +++---
>   arch/x86/kernel/idt.c              |  1 -
>   arch/x86/kernel/smp.c              |  9 ---------
>   arch/x86/xen/smp.c                 | 22 +--------------------
>   8 files changed, 23 insertions(+), 57 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
> index 854899bfec5d..661e125ed936 100644
> --- a/arch/x86/entry/entry_fred.c
> +++ b/arch/x86/entry/entry_fred.c
> @@ -114,7 +114,6 @@ static idtentry_t sysvec_table[NR_SYSTEM_VECTORS] __ro_after_init = {
>   
>   	SYSVEC(RESCHEDULE_VECTOR,		reschedule_ipi),
>   	SYSVEC(CALL_FUNCTION_SINGLE_VECTOR,	call_function_single),
> -	SYSVEC(CALL_FUNCTION_VECTOR,		call_function),
>   	SYSVEC(REBOOT_VECTOR,			reboot),
>   
>   	SYSVEC(THRESHOLD_APIC_VECTOR,		threshold),
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index f400cfac69a6..d429a2720e8e 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -679,7 +679,6 @@ DECLARE_IDTENTRY_SYSVEC(X86_PLATFORM_IPI_VECTOR,	sysvec_x86_platform_ipi);
>   DECLARE_IDTENTRY(RESCHEDULE_VECTOR,			sysvec_reschedule_ipi);
>   DECLARE_IDTENTRY_SYSVEC(REBOOT_VECTOR,			sysvec_reboot);
>   DECLARE_IDTENTRY_SYSVEC(CALL_FUNCTION_SINGLE_VECTOR,	sysvec_call_function_single);
> -DECLARE_IDTENTRY_SYSVEC(CALL_FUNCTION_VECTOR,		sysvec_call_function);
>   #else
>   # define fred_sysvec_reschedule_ipi			NULL
>   # define fred_sysvec_reboot				NULL
> diff --git a/arch/x86/include/asm/irq_vectors.h b/arch/x86/include/asm/irq_vectors.h
> index 85253fc8e384..ca8f2045f915 100644
> --- a/arch/x86/include/asm/irq_vectors.h
> +++ b/arch/x86/include/asm/irq_vectors.h
> @@ -44,10 +44,10 @@
>   #define ISA_IRQ_VECTOR(irq)		(((FIRST_EXTERNAL_VECTOR + 16) & ~15) + irq)
>   
>   /*
> - * Special IRQ vectors used by the SMP architecture, 0xf0-0xff
> + * Special IRQ vectors used by the SMP architecture, 0xec-0xff
>    *
>    *  some of the following vectors are 'rare', they are merged
> - *  into a single vector (CALL_FUNCTION_VECTOR) to save vector space.
> + *  into a single vector to save vector space.
>    *  TLB, reschedule and local APIC vectors are performance-critical.
>    */
>   
> @@ -61,49 +61,48 @@
>   
>   #define ERROR_APIC_VECTOR		0xfe
>   #define RESCHEDULE_VECTOR		0xfd
> -#define CALL_FUNCTION_VECTOR		0xfc
> -#define CALL_FUNCTION_SINGLE_VECTOR	0xfb
> -#define THERMAL_APIC_VECTOR		0xfa
> -#define THRESHOLD_APIC_VECTOR		0xf9
> -#define REBOOT_VECTOR			0xf8
> +#define CALL_FUNCTION_SINGLE_VECTOR	0xfc
> +#define THERMAL_APIC_VECTOR		0xfb
> +#define THRESHOLD_APIC_VECTOR		0xfa
> +#define REBOOT_VECTOR			0xf9
>   
>   /*
>    * Generic system vector for platform specific use
>    */
> -#define X86_PLATFORM_IPI_VECTOR		0xf7
> +#define X86_PLATFORM_IPI_VECTOR		0xf8
>   
>   /*
>    * IRQ work vector:
>    */
> -#define IRQ_WORK_VECTOR			0xf6
> +#define IRQ_WORK_VECTOR			0xf7
>   
>   /* IRQ vector for PMIs when running a guest with a mediated PMU. */
> -#define PERF_GUEST_MEDIATED_PMI_VECTOR	0xf5
> +#define PERF_GUEST_MEDIATED_PMI_VECTOR	0xf6
>   
> -#define DEFERRED_ERROR_VECTOR		0xf4
> +#define DEFERRED_ERROR_VECTOR		0xf5
>   
>   /* Vector on which hypervisor callbacks will be delivered */
> -#define HYPERVISOR_CALLBACK_VECTOR	0xf3
> +#define HYPERVISOR_CALLBACK_VECTOR	0xf4
>   
>   /* Vector for KVM to deliver posted interrupt IPI */
> -#define POSTED_INTR_VECTOR		0xf2
> -#define POSTED_INTR_WAKEUP_VECTOR	0xf1
> -#define POSTED_INTR_NESTED_VECTOR	0xf0
> +#define POSTED_INTR_VECTOR		0xf3
> +#define POSTED_INTR_WAKEUP_VECTOR	0xf2
> +#define POSTED_INTR_NESTED_VECTOR	0xf1
>   
> -#define MANAGED_IRQ_SHUTDOWN_VECTOR	0xef
> +#define MANAGED_IRQ_SHUTDOWN_VECTOR	0xf0
>   
>   #if IS_ENABLED(CONFIG_HYPERV)
> -#define HYPERV_REENLIGHTENMENT_VECTOR	0xee
> -#define HYPERV_STIMER0_VECTOR		0xed
> +#define HYPERV_REENLIGHTENMENT_VECTOR	0xef
> +#define HYPERV_STIMER0_VECTOR		0xee
>   #endif
>   
> -#define LOCAL_TIMER_VECTOR		0xec
> +#define LOCAL_TIMER_VECTOR		0xed
>   
>   /*
>    * Posted interrupt notification vector for all device MSIs delivered to
>    * the host kernel.
>    */
> -#define POSTED_MSI_NOTIFICATION_VECTOR	0xeb
> +#define POSTED_MSI_NOTIFICATION_VECTOR	0xec
>   
>   #define NR_VECTORS			 256
>   
> diff --git a/arch/x86/include/asm/xen/events.h b/arch/x86/include/asm/xen/events.h
> index 62bdceb594f1..11eeceb91fd6 100644
> --- a/arch/x86/include/asm/xen/events.h
> +++ b/arch/x86/include/asm/xen/events.h
> @@ -6,7 +6,6 @@
>   
>   enum ipi_vector {
>   	XEN_RESCHEDULE_VECTOR,
> -	XEN_CALL_FUNCTION_VECTOR,
>   	XEN_CALL_FUNCTION_SINGLE_VECTOR,
>   	XEN_SPIN_UNLOCK_VECTOR,
>   	XEN_IRQ_WORK_VECTOR,
> diff --git a/arch/x86/kernel/apic/ipi.c b/arch/x86/kernel/apic/ipi.c
> index c627bee3b14f..499bb3b8803b 100644
> --- a/arch/x86/kernel/apic/ipi.c
> +++ b/arch/x86/kernel/apic/ipi.c
> @@ -88,14 +88,14 @@ void native_send_call_func_ipi(const struct cpumask *mask)
>   			goto sendmask;
>   
>   		if (cpumask_test_cpu(cpu, mask))
> -			__apic_send_IPI_all(CALL_FUNCTION_VECTOR);
> +			__apic_send_IPI_all(CALL_FUNCTION_SINGLE_VECTOR);
>   		else if (num_online_cpus() > 1)
> -			__apic_send_IPI_allbutself(CALL_FUNCTION_VECTOR);
> +			__apic_send_IPI_allbutself(CALL_FUNCTION_SINGLE_VECTOR);
>   		return;
>   	}
>   
>   sendmask:
> -	__apic_send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
> +	__apic_send_IPI_mask(mask, CALL_FUNCTION_SINGLE_VECTOR);
>   }
>   
>   void apic_send_nmi_to_offline_cpu(unsigned int cpu)
> diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
> index 90a22e24a9eb..b48e0e33ff03 100644
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -133,7 +133,6 @@ static const struct idt_data ia32_idt[] __initconst = {
>   static const __initconst struct idt_data apic_idts[] = {
>   #ifdef CONFIG_SMP
>   	INTG(RESCHEDULE_VECTOR,			asm_sysvec_reschedule_ipi),
> -	INTG(CALL_FUNCTION_VECTOR,		asm_sysvec_call_function),
>   	INTG(CALL_FUNCTION_SINGLE_VECTOR,	asm_sysvec_call_function_single),
>   	INTG(REBOOT_VECTOR,			asm_sysvec_reboot),
>   #endif
> diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
> index 985103cab16c..c7397816b311 100644
> --- a/arch/x86/kernel/smp.c
> +++ b/arch/x86/kernel/smp.c
> @@ -255,15 +255,6 @@ DEFINE_IDTENTRY_SYSVEC_SIMPLE(sysvec_reschedule_ipi)
>   	trace_reschedule_exit(RESCHEDULE_VECTOR);
>   }
>   
> -DEFINE_IDTENTRY_SYSVEC(sysvec_call_function)
> -{
> -	apic_eoi();
> -	trace_call_function_entry(CALL_FUNCTION_VECTOR);
> -	inc_irq_stat(CALL_FUNCTION);
> -	generic_smp_call_function_interrupt();
> -	trace_call_function_exit(CALL_FUNCTION_VECTOR);
> -}
> -
>   DEFINE_IDTENTRY_SYSVEC(sysvec_call_function_single)
>   {
>   	apic_eoi();
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 05ee0d3b0874..d5544026ede5 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -11,7 +11,6 @@
>   #include "xen-ops.h"
>   
>   static DEFINE_PER_CPU(struct xen_common_irq, xen_resched_irq) = { .irq = -1 };
> -static DEFINE_PER_CPU(struct xen_common_irq, xen_callfunc_irq) = { .irq = -1 };
>   static DEFINE_PER_CPU(struct xen_common_irq, xen_callfuncsingle_irq) = { .irq = -1 };
>   static DEFINE_PER_CPU(struct xen_common_irq, xen_debug_irq) = { .irq = -1 };
>   
> @@ -37,12 +36,6 @@ void xen_smp_intr_free(unsigned int cpu)
>   		unbind_from_irqhandler(per_cpu(xen_resched_irq, cpu).irq, NULL);
>   		per_cpu(xen_resched_irq, cpu).irq = -1;
>   	}
> -	kfree(per_cpu(xen_callfunc_irq, cpu).name);
> -	per_cpu(xen_callfunc_irq, cpu).name = NULL;
> -	if (per_cpu(xen_callfunc_irq, cpu).irq >= 0) {
> -		unbind_from_irqhandler(per_cpu(xen_callfunc_irq, cpu).irq, NULL);
> -		per_cpu(xen_callfunc_irq, cpu).irq = -1;
> -	}
>   	kfree(per_cpu(xen_debug_irq, cpu).name);
>   	per_cpu(xen_debug_irq, cpu).name = NULL;
>   	if (per_cpu(xen_debug_irq, cpu).irq >= 0) {
> @@ -80,16 +73,6 @@ int xen_smp_intr_init(unsigned int cpu)
>   	callfunc_name = kasprintf(GFP_KERNEL, "callfunc%d", cpu);
>   	if (!callfunc_name)
>   		goto fail_mem;
> -	per_cpu(xen_callfunc_irq, cpu).name = callfunc_name;
> -	rc = bind_ipi_to_irqhandler(XEN_CALL_FUNCTION_VECTOR,
> -				    cpu,
> -				    xen_call_function_interrupt,
> -				    IRQF_PERCPU|IRQF_NOBALANCING,
> -				    callfunc_name,
> -				    NULL);
> -	if (rc < 0)
> -		goto fail;
> -	per_cpu(xen_callfunc_irq, cpu).irq = rc;
>   
>   	if (!xen_fifo_events) {
>   		debug_name = kasprintf(GFP_KERNEL, "debug%d", cpu);
> @@ -154,7 +137,7 @@ void xen_smp_send_call_function_ipi(const struct cpumask *mask)
>   {
>   	int cpu;
>   
> -	__xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_VECTOR);
> +	__xen_send_IPI_mask(mask, XEN_CALL_FUNCTION_SINGLE_VECTOR);
>   
>   	/* Make sure other vcpus get a chance to run if they need to. */
>   	for_each_cpu(cpu, mask) {
> @@ -179,9 +162,6 @@ static inline int xen_map_vector(int vector)
>   	case RESCHEDULE_VECTOR:
>   		xen_vector = XEN_RESCHEDULE_VECTOR;
>   		break;
> -	case CALL_FUNCTION_VECTOR:
> -		xen_vector = XEN_CALL_FUNCTION_VECTOR;
> -		break;
>   	case CALL_FUNCTION_SINGLE_VECTOR:
>   		xen_vector = XEN_CALL_FUNCTION_SINGLE_VECTOR;
>   		break;


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