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

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Date:	Fri, 25 Jul 2008 13:12:44 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Mike Travis <travis@....com>
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

Mike Travis wrote:
> Jeremy Fitzhardinge wrote:
> ...
>   
>> Last time it was doing this, it was a result of a triple-fault caused by
>> loading %ds with an all-zero gdt.  I modified Xen to dump the CPU state
>> on triple-faults, so it was easy to pinpoint.  I can do that again if it
>> helps.
>>
>>    J
>>     
>
> Hi Jeremy,
>
> There are two question marks for my patchset.  The first is in
>
> arch/x86/xen/smp.c:xen_cpu_up()
>
> 287 #ifdef CONFIG_X86_64
> 288         /* Allocate node local memory for AP pdas */
> 289         WARN_ON(cpu == 0);
> 290         if (cpu > 0) {
> 291                 rc = get_local_pda(cpu);
> 292                 if (rc)
> 293                         return rc;
> 294         }
> 295 #endif
>
> and the second is at:
>
> arch/x86/xen/enlighten.c:xen_start_kernel()
>
> 1748 #ifdef CONFIG_X86_64
> 1749         /* Disable until direct per-cpu data access. */
> 1750         have_vcpu_info_placement = 0;
> 1751         x86_64_init_pda();
> 1752 #endif
>
> I believe with the pda folded into the percpu area, get_local_pda()
> and x86_64_init_pda() have been removed, so these are no longer
> required, yes?
>   

Well, presumably they need to be replaced with whatever setup you need 
to do now.

xen_start_kernel() is the first function called after a Xen kernel boot, 
and so it must make sure the early percpu setup is done before it can 
start using percpu variables.

xen_cpu_up() needs to do whatever initialization needed for a new cpu's 
percpu area (presumably whatever do_boot_cpu() does).

> Also, arch/x86/kernel/acpi/sleep.c:acpi_save_state_mem() sets up
> the startup code address with:
>
> 102         initial_code = (unsigned long)wakeup_long64;
> 103         saved_magic = 0x123456789abcdef0;
>
> Should the pda and gdt_page address also be setup as is done in
> smpboot.c:do_boot_cpu():
>
> (CONFIG_X86_64)
>  801         initial_pda = (unsigned long)get_cpu_pda(cpu);
>  802 #endif
>  803         early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
>  804         initial_code = (unsigned long)start_secondary;
>   
I don't think so.  It looks like it's doing its own gdt save/restore.

    J
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