> Mike Travis wrote:
>> Ingo Molnar wrote:
>>
>>> * Mike Travis <travis@sgi.com> wrote:
>>>
>>>
>>>> * Declare the pda as a per cpu variable.
>>>>
>>>> * Make the x86_64 per cpu area start at zero.
>>>>
>>>> * Since the pda is now the first element of the per_cpu area,
>>>> cpu_pda()
>>>> is no longer needed and per_cpu() can be used instead. This
>>>> also makes
>>>> the _cpu_pda[] table obsolete.
>>>>
>>>> * Since %gs is pointing to the pda, it will then also point to the
>>>> per cpu
>>>> variables and can be accessed thusly:
>>>>
>>>> %gs:[&per_cpu_xxxx - __per_cpu_start]
>>>>
>>>> Based on linux-2.6.tip
>>>>
>>> -tip testing found an instantaneous reboot crash on 64-bit x86, with
>>> this config:
>>>
>>>
http://redhat.com/~mingo/misc/config-Thu_Jun__5_11_43_51_CEST_2008.bad
>>>
>>
>> I'm still stuck on this one. One new development is that the current
>> -tip
>> branch without the patches boots to the kernel prompt then hangs after
>> a few
>> moments and then reboots. It seems you can tickle it using ^C to abort a
>> process.
>
> Hi Mike,
>
> I added some instrumentation to Xen to print the cpu state on
> triple-fault, which highlights an obvious-looking problem.
>
> (XEN) hvm.c:767:d1 Triple fault on VCPU0 - invoking HVM system reset.
> (XEN) ----[ Xen-3.3-unstable x86_64 debug=y Not tainted ]----
> (XEN) CPU: 1
> (XEN) RIP: 0010:[<ffffffff80200160>]
> (XEN) RFLAGS: 0000000000010002 CONTEXT: hvm
> (XEN) rax: 0000000000000018 rbx: 0000000000000000 rcx: 00000000c0000080
> (XEN) rdx: 0000000000000000 rsi: 0000000000092f40 rdi: 0000000020100800
> (XEN) rbp: 0000000000000000 rsp: ffffffff807dfff8 r8: 0000000000208000
> (XEN) r9: 0000000000000000 r10: 0000000000000000 r11: 00000000000000de
> (XEN) r12: 0000000000000000 r13: 0000000000000000 r14: 0000000000000000
> (XEN) r15: 0000000000000000 cr0: 0000000080050033 cr4: 00000000000000a0
> (XEN) cr3: 0000000000201000 cr2: 0000000000000000
> (XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: 0000 cs: 0010
>
> The rip is:
>
> (gdb) x/i 0xffffffff80200160
> 0xffffffff80200160 <secondary_startup_64+96>: movl %eax,%ds
>
> which is:
>
> lgdt early_gdt_descr(%rip)
>
> /* set up data segments. actually 0 would do too */
> movl $__KERNEL_DS,%eax
> movl %eax,%ds
> movl %eax,%ss
> movl %eax,%es
>
> And early_gdt_descr is:
>
> .globl early_gdt_descr
> early_gdt_descr:
> .word GDT_ENTRIES*8-1
> .quad per_cpu__gdt_page
>
> and per_cpu__gdt_page is zero-based, and therefore not a directly
> addressable symbol.
>
> I tried this patch, but it didn't work. Perhaps I'm missing something.
>
> diff -r bf5a46e13f78 arch/x86/kernel/head_64.S
> --- a/arch/x86/kernel/head_64.S Tue Jun 17 22:10:51 2008 -0700
> +++ b/arch/x86/kernel/head_64.S Wed Jun 18 10:34:24 2008 -0700
> @@ -94,6 +94,8 @@
>
> addq %rbp, level2_fixmap_pgt + (506*8)(%rip)
>
> + addq $__per_cpu_load, early_gdt_descr+2(%rip)
> +
> /* Add an Identity mapping if I am above 1G */
> leaq _text(%rip), %rdi
> andq $PMD_PAGE_MASK, %rdi
>
>
> J
