linux-kernel - Re: [patch v3 1/7] x86/smp: Make stop_other

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Date:   Mon, 19 Jun 2023 10:51:39 -0700
From:   Ashok Raj <ashok.raj@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Mario Limonciello <mario.limonciello@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Tony Battersby" <tonyb@...ernetics.com>,
        Ashok Raj <ashok.raj@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [patch v3 1/7] x86/smp: Make stop_other_cpus() more robust

On Fri, Jun 16, 2023 at 01:57:59PM -0700, Ashok Raj wrote:
> On Fri, Jun 16, 2023 at 08:01:56PM +0200, Thomas Gleixner wrote:
> > On Fri, Jun 16 2023 at 07:13, Ashok Raj wrote:
> > > On Fri, Jun 16, 2023 at 09:53:25AM +0200, Thomas Gleixner wrote:
> > >> > can we simplify this by just apic->send_IPI(cpu, NMI_VECTOR); ??
> > >> 
> > >> That would not set APIC_DM_NMI in delivery mode and the IPI would be
> > >> sent with APIC_DM_FIXED.
> > >
> > > That's correct. 
> > >
> > > Maybe if we use apic->send_IPI_mask(cpumask_of(cpu), NMI_VECTOR)
> > >
> > > apic->send_IPI_mask(cpumask_of(cpu),NMI_VECTOR)
> > >    __x2apic_send_IPI_mask() 
> > >       __x2apic_send_IPI_dest()
> > > 	  unsigned long cfg = __prepare_ICR(0, vector, dest);
> > > 	  native_x2apic_icr_write(cfg, apicid);
> > >
> > > __prepare_ICR() seems to have the magic for APIC_DM_NMI?
> > 
> > Bah. I clearly neither can read nor can remember any of the internals of
> > that code:
> > 
> > apic->send_IPI()
> >   x2apic_send_IPI()
> >     __x2apic_send_IPI_dest()
> > 
> > It also works for all other APIC incarnations. 
> 
> Works!
> 

Forgot to add 

Reviewed-by: Ashok Raj <ashok.raj@...el.com>