linux-kernel - Re: [patch 5/6] x86/smp: Split sending INIT IPI out into a helper function

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Date:   Sun, 4 Jun 2023 07:02:33 +0300
From:   Mika Penttilä <mika.penttila@...sol.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Ashok Raj <ashok.raj@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [patch 5/6] x86/smp: Split sending INIT IPI out into a helper
 function

Hi,

On 3.6.2023 23.07, Thomas Gleixner wrote:
> Putting CPUs into INIT is a safer place during kexec() to park CPUs.
> 
> Split the INIT assert/deassert sequence out so it can be reused.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   arch/x86/kernel/smpboot.c |   51 +++++++++++++++++++---------------------------
>   1 file changed, 22 insertions(+), 29 deletions(-)
> 
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -853,47 +853,40 @@ wakeup_secondary_cpu_via_nmi(int apicid,
>   	return (send_status | accept_status);
>   }
>   
> -static int
> -wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
> +static void send_init_sequence(int phys_apicid)
>   {
> -	unsigned long send_status = 0, accept_status = 0;
> -	int maxlvt, num_starts, j;
> -
> -	maxlvt = lapic_get_maxlvt();
> +	int maxlvt = lapic_get_maxlvt();
>   
> -	/*
> -	 * Be paranoid about clearing APIC errors.
> -	 */
> +	/* Be paranoid about clearing APIC errors. */
>   	if (APIC_INTEGRATED(boot_cpu_apic_version)) {
> -		if (maxlvt > 3)		/* Due to the Pentium erratum 3AP.  */
> +		/* Due to the Pentium erratum 3AP.  */
> +		if (maxlvt > 3)
>   			apic_write(APIC_ESR, 0);
>   		apic_read(APIC_ESR);
>   	}
>   
> -	pr_debug("Asserting INIT\n");
> -
> -	/*
> -	 * Turn INIT on target chip
> -	 */
> -	/*
> -	 * Send IPI
> -	 */
> -	apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT,
> -		       phys_apicid);
> -
> -	pr_debug("Waiting for send to finish...\n");
> -	send_status = safe_apic_wait_icr_idle();
> +	/* Assert INIT on the target CPU */
> +	apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT, phys_apicid);
> +	safe_apic_wait_icr_idle();
>   
>   	udelay(init_udelay);
>   
> -	pr_debug("Deasserting INIT\n");
> -
> -	/* Target chip */
> -	/* Send IPI */
> +	/* Deassert INIT on the target CPU */
>   	apic_icr_write(APIC_INT_LEVELTRIG | APIC_DM_INIT, phys_apicid);
> +	safe_apic_wait_icr_idle();
> +}
> +
> +/*
> + * Wake up AP by INIT, INIT, STARTUP sequence.
> + */
> +static int wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
> +{
> +	unsigned long send_status = 0, accept_status = 0;
> +	int maxlvt, num_starts, j;
> +
> +	preempt_disable();

This seems like an unbalanced preempt disable..

>   
> -	pr_debug("Waiting for send to finish...\n");
> -	send_status = safe_apic_wait_icr_idle();
> +	send_init_sequence(phys_apicid);
>   
>   	mb();
>   
> 


--Mika