linux-kernel - Re: [PATCH] x86: enable x2apic early at the first point

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Message-ID: <49A083A2.30303@kernel.org>
Date:	Sat, 21 Feb 2009 14:43:46 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: enable x2apic early at the first point

Suresh Siddha wrote:
> On Fri, 2009-02-20 at 01:55 -0800, Ingo Molnar wrote:
>> * Ingo Molnar <mingo@...e.hu> wrote:
>>
>>>>  arch/x86/kernel/apic/apic.c           |    3 +--
>>>>  arch/x86/kernel/apic/x2apic_cluster.c |    5 ++++-
>>>>  arch/x86/kernel/apic/x2apic_phys.c    |    5 ++++-
>>>>  arch/x86/kernel/apic/x2apic_uv_x.c    |    4 +++-
>>>>  drivers/pci/dmar.c                    |    3 ++-
>>>>  5 files changed, 14 insertions(+), 6 deletions(-)
>>> I've applied it because it fixes a real bug, but this code 
>>> really needs a cleanup. Look at the repeat patterns:
>> unapplied it again as it breaks the build:
>>
>> arch/x86/kernel/apic/x2apic_cluster.c: In function 'x2apic_acpi_madt_oem_check':
>> arch/x86/kernel/apic/x2apic_cluster.c:17: error: 'disable_x2apic' undeclared (first use in this function)
>> arch/x86/kernel/apic/x2apic_cluster.c:17: error: (Each undeclared identifier is reported only once
>> arch/x86/kernel/apic/x2apic_cluster.c:17: error: for each function it appears in.)
>>
>> so please resend the fixed and cleaned up version.
> 
> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: x86: select x2apic ops in early apic probe only if x2apic mode is enabled
> 
> If BIOS hands over the control to OS in legacy xapic mode, select legacy xapic
> related ops in the early apic probe and shift to x2apic ops later in the boot
> sequence, only after enabling x2apic mode.
> 
> If BIOS hands over the control in x2apic mode, select x2apic related ops
> in the early apic probe.
> 
> This fixes the early boot panic, where we were selecting x2apic ops,
> while the cpu is still in legacy xapic mode.

good, other than that.

for x2apic preenabled system,
when nox2apic is used, cpu_has_x2apic will be cleared, apic will be xapic phys_flat or flat.
is that expected?

should
1. ignore nox2apic
2. or try to disable x2apic?

YH
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