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Date:   Fri, 16 Jun 2023 13:57:59 -0700
From:   Ashok Raj <ashok.raj@intel.com>
To:     Thomas Gleixner <tglx@linutronix.de>
CC:     LKML <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "Tony Battersby" <tonyb@cybernetics.com>,
        Ashok Raj <ashok.raj@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Arjan van de Veen <arjan@linux.intel.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Ashok Raj <ashok.raj@intel.com>
Subject: Re: [patch v3 1/7] x86/smp: Make stop_other_cpus() more robust
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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!