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Subject: Re: [PATCH] Use x2apic_supported() in the default_apic_id_valid()
 function.
From: Suresh Siddha <suresh.b.siddha@intel.com>
Reply-To: Suresh Siddha <suresh.b.siddha@intel.com>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Steffen Persvold <sp@numascale.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Daniel J Blueman <daniel@numascale-asia.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org
Date: Thu, 15 Mar 2012 14:21:44 -0700
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On Thu, 2012-03-15 at 13:23 -0700, Yinghai Lu wrote:
> On Thu, Mar 15, 2012 at 11:03 AM, Steffen Persvold <sp@numascale.com> wrote:
> > Use x2apic_supported() in the default_apic_id_valid() function. If x2apic mode is disabled (via nox2apic for example), x2apic_supported() will return false.
> >
> > This allows us to substitute the check in arch/x86/kernel/acpi/boot.c::acpi_parse_x2apic and avoid feigning the x2apic cpu feature in the NumaChip apic code.
> >
> > Signed-off-by: Steffen Persvold <sp@numascale.com>
> > Reviewed-by: Daniel J Blueman <daniel@numascale-asia.com>
> 
> I double checked on system with x2apic preenabled,
> nox2apic in boot command line still works well and it
> skips starting APs with apic id > 255.
> 
> Acked-by: Yinghai Lu <yinghai@kernel.org>

This breaks the smpboot check if enabling interrupt-remapping/x2apic
fails on a platform. We will be in xapic mode and we don't clear the
x2apic cpufeature bit in this case and as such smpboot check will fail.

So this change breaks the commit
c284b42abadbb22083bfde24d308899c08d44ffa.

I think the right thing is to have two different apid_id_valid checks
one for xapic driver (apic_flat_64.c) and another for x2apic driver
(x2apic_phys/cluster.c) and that way, x2apic MADT entries will be parsed
only if bios has handed over the OS in x2apic mode or if we have
selected the numachip model.

thanks,
suresh