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    Subject[PATCH] [28/40] i386: Fix UP gdt bugs
    Date

    From: Jeremy Fitzhardinge <jeremy@goop.org>
    Fixes two problems with the GDT when compiling for uniprocessor:
    - There's no percpu segment, so trying to load its selector into %fs fails.
    Use a null selector instead.
    - The real gdt needs to be loaded at some point. Do it in cpu_init().

    Signed-off-by: Chris Wright <chrisw@sous-sol.org>
    Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
    Signed-off-by: Andi Kleen <ak@suse.de>
    Cc: Rusty Russell <rusty@rustcorp.com.au>

    ---
    arch/i386/kernel/cpu/common.c | 13 +++++++++++++
    arch/i386/kernel/smpboot.c | 12 ------------
    include/asm-i386/processor.h | 1 +
    include/asm-i386/segment.h | 4 ++++
    4 files changed, 18 insertions(+), 12 deletions(-)

    ===================================================================
    Index: linux/arch/i386/kernel/cpu/common.c
    ===================================================================
    --- linux.orig/arch/i386/kernel/cpu/common.c
    +++ linux/arch/i386/kernel/cpu/common.c
    @@ -638,6 +638,18 @@ struct pt_regs * __devinit idle_regs(str
    return regs;
    }

    +/* Current gdt points %fs at the "master" per-cpu area: after this,
    + * it's on the real one. */
    +void switch_to_new_gdt(void)
    +{
    + struct Xgt_desc_struct gdt_descr;
    +
    + gdt_descr.address = (long)get_cpu_gdt_table(smp_processor_id());
    + gdt_descr.size = GDT_SIZE - 1;
    + load_gdt(&gdt_descr);
    + asm("mov %0, %%fs" : : "r" (__KERNEL_PERCPU) : "memory");
    +}
    +
    /*
    * cpu_init() initializes state that is per-CPU. Some data is already
    * initialized (naturally) in the bootstrap process, such as the GDT
    @@ -668,6 +680,7 @@ void __cpuinit cpu_init(void)
    }

    load_idt(&idt_descr);
    + switch_to_new_gdt();

    /*
    * Set up and load the per-CPU TSS and LDT
    Index: linux/arch/i386/kernel/smpboot.c
    ===================================================================
    --- linux.orig/arch/i386/kernel/smpboot.c
    +++ linux/arch/i386/kernel/smpboot.c
    @@ -1177,18 +1177,6 @@ void __init native_smp_prepare_cpus(unsi
    smp_boot_cpus(max_cpus);
    }

    -/* Current gdt points %fs at the "master" per-cpu area: after this,
    - * it's on the real one. */
    -static inline void switch_to_new_gdt(void)
    -{
    - struct Xgt_desc_struct gdt_descr;
    -
    - gdt_descr.address = (long)get_cpu_gdt_table(smp_processor_id());
    - gdt_descr.size = GDT_SIZE - 1;
    - load_gdt(&gdt_descr);
    - asm("mov %0, %%fs" : : "r" (__KERNEL_PERCPU) : "memory");
    -}
    -
    void __init native_smp_prepare_boot_cpu(void)
    {
    unsigned int cpu = smp_processor_id();
    Index: linux/include/asm-i386/processor.h
    ===================================================================
    --- linux.orig/include/asm-i386/processor.h
    +++ linux/include/asm-i386/processor.h
    @@ -750,6 +750,7 @@ extern void enable_sep_cpu(void);
    extern int sysenter_setup(void);

    extern void cpu_set_gdt(int);
    +extern void switch_to_new_gdt(void);
    extern void cpu_init(void);

    extern int force_mwait;
    Index: linux/include/asm-i386/segment.h
    ===================================================================
    --- linux.orig/include/asm-i386/segment.h
    +++ linux/include/asm-i386/segment.h
    @@ -75,7 +75,11 @@
    #define __ESPFIX_SS (GDT_ENTRY_ESPFIX_SS * 8)

    #define GDT_ENTRY_PERCPU (GDT_ENTRY_KERNEL_BASE + 15)
    +#ifdef CONFIG_SMP
    #define __KERNEL_PERCPU (GDT_ENTRY_PERCPU * 8)
    +#else
    +#define __KERNEL_PERCPU 0
    +#endif

    #define GDT_ENTRY_DOUBLEFAULT_TSS 31

    -
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