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 03:24:01 -0700
From:   Ashok Raj <ashok_raj@...ux.intel.com>
To:     Mika Penttilä <mika.penttila@...sol.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, 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>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [patch 5/6] x86/smp: Split sending INIT IPI out into a helper
 function

Hi

On Sun, Jun 04, 2023 at 07:02:33AM +0300, Mika Penttilä wrote:
> 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;

Also maxlvt used uninitialized.

> > +
> > +	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
>