Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpuarea

[Jeremy Fitzhardinge]

Mike Travis wrote:
> Jeremy Fitzhardinge wrote:
>   
> > Mike Travis wrote:
> >     
> > > Ingo Molnar wrote:
> > >  
> > >       
> > > > * Mike Travis <travis@xxxxxxx> 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
> >     
>
> Hi Jeremy,
>
> I'm not finding that code in the tip/latest or linux-next branches... ?
>   

You mean your percpu/pda code?  No, I'm carrying it locally because I 
need it as a base for my Xen work.  Xen bypasses these early boot 
stages, so I haven't seen any problems so far.
But I'd also like to make sure that my Xen changes don't break native 
boots, too...

> I can send you my latest version of the patch which is better than
> the previous but still is having problems with the config file that
> Ingo sent out.  (It also has a weird quirk that it will hang and
> reboot after about 30 seconds with or without my patch.)
>   

Yes, keep me uptodate with the percpu work.

   J
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