linux-kernel - Re: [PATCH] x86: fix x2apic preenabled system with kexec

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Message-ID: <4C3F7222.5040404@kernel.org>
Date:	Thu, 15 Jul 2010 13:40:02 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	stable <stable@...nel.org>
Subject: Re: [PATCH] x86: fix x2apic preenabled system with kexec

On 07/15/2010 01:10 PM, Yinghai Lu wrote:
> On 07/15/2010 11:16 AM, Suresh Siddha wrote:
>> On Thu, 2010-07-15 at 00:00 -0700, Yinghai Lu wrote:
>>
>>> BTW: is there any x2apic preenabled system with apicid of boot cpu > 255?
>>
>> I am not sure. There might be one. Is there any bug which can't handle
>> this condition?
> 
> We merged apic_ops into struct apic a while ago.
> 
> so even for system with x2apic preenabled by BIOS, x2apic_cluster/phys is set to apic until smp_pare_cpus()::default_setup_apic_routing() after enable_IR_x2apic.
> 
> that means the boot cpu x2apic is accessed via memmap instead msr based way at that point.
> 
> not sure if the Boot apic id is bigger than 255. read_apic() for apic id could be wrong. ( in early_acpi_boot_init, acpi_boot_init, init_apic_mappings)
> 
> looks like we need to re-read boot_cpu_physical_apicid
> or we could assign x2apic_cluster/phys in check_x2apic(), and later if intr_remapping can not be enabed, we can revert back to phys_flat or flat?
> 

never mind,

early_acpi_boot_init::acpi_parse_madt::default_acpi_madt_oem_check() will handle the case.
it will set the apic to apic_x2apic_... accordingly if x2apic is preenabled.

Thanks

Yinghai
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