Messages in this thread | | | Date | Fri, 20 Jun 2008 11:30:20 -0700 | From | Mike Travis <> | Subject | Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area |
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Christoph Lameter wrote: > On Fri, 20 Jun 2008, Jeremy Fitzhardinge wrote: > >> So it seems the problem is that the pre-initialized gdt_page is being lost and >> replaced with zero. Linker script bug? > > Is the pre initialized gdt page in the per cpu area? Does not look like > it. The loader setup for the percpu section changes with zero basing. > Maybe that has bad side effects?
Yes, it is... The fixup logic is this:
0000000000004000 D per_cpu__gdt_page ffffffff81911000 A __per_cpu_load
arch/x86/kernel/cpu/common.c:
DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = { [GDT_ENTRY_KERNEL_CS] = { { { 0x0000ffff, 0x00cf9a00 } } }, ...
arch/x86/kernel/head_64.S:
startup_64: ... /* * Fix up per_cpu__gdt_page offset when basing percpu * variables at zero. This is only needed for the boot cpu. */ addq $__per_cpu_load, early_gdt_descr_base(%rip)
ENTRY(secondary_startup_64) ... /* * We must switch to a new descriptor in kernel space for the GDT * because soon the kernel won't have access anymore to the userspace * addresses where we're currently running on. We have to do that here * because in 32bit we couldn't load a 64bit linear address. */ lgdt early_gdt_descr(%rip) ... .globl early_gdt_descr early_gdt_descr: .word GDT_ENTRIES*8-1 early_gdt_descr_base: .quad per_cpu__gdt_page
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