Messages in this thread Patch in this message | | | Date | Wed, 18 Jun 2008 10:36:40 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area |
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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
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