linux-kernel - Re: [crash, bisected] Re: [PATCH 3/4] x86

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Message-ID: <488A4007.2000002@sgi.com>
Date:	Fri, 25 Jul 2008 14:05:11 -0700
From:	Mike Travis <travis@....com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>
Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu
 area


Ok, I'll just post what I have now (compiles and boots cleanly)...  and then
we can discuss these more extensively.

Thanks,
Mike

Jeremy Fitzhardinge wrote:
> Mike Travis wrote:
>> Is this for the boot cpu (0), or for all cpus?  For the boot cpu, I have
>> this now in arch/x86/kernel/setup_percpu.c:
>>
>> +#ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU
>> +
>> +/* Initialize percpu offset for boot cpu (0) */
>> +unsigned long __per_cpu_offset[NR_CPUS] __read_mostly = {
>> +       [0] = (unsigned long)__per_cpu_load
>> +};
>> +#else
>>  unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
>> +#endif
>>
>> So this should apply as well to the xen startup?
>>   
> 
> If it's just a static initialization, then it should be fine.  But some
> equivalent of your head_64.S changes are needed to actually set things up?
> 
> 
>>> xen_cpu_up() needs to do whatever initialization needed for a new cpu's
>>> percpu area (presumably whatever do_boot_cpu() does).
>>>
>>>     
>>
>> Does the startup include executing
>> arch/x86/kernel/head_64.S:startup_64() ?
>> I see arch/x86/xen/xen-head.S:startup_xen() so I'm guessing not?
>>   
> 
> No, it doesn't.  It bypasses all that startup code.  Aside from the few
> instructions in xen-head.S, xen_start_kernel() is the first thing to get
> run.
> 
> But when bringing up a secondary cpu, where does the new percpu memory
> actually get allocated?
> 
>> For the real startup, I do the following two things.  But I'm not
>> comfortable
>> enough with xen to think I'll get it right putting this in xen-head.S.
>>   
> 
> Yes, it needn't be in the asm code.  I'll work out what to do.  Looks
> like I just need to do an appropriate wrmsr(MSR_GS_BASE, ).
> 
>    J

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