Messages in this thread | | | Date | Wed, 22 Feb 2006 10:08:50 -0800 | From | Zachary Amsden <> | Subject | Re: [PATCH] fix broken x86 SMP boot sequence |
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James Bottomley wrote:
>This patch: > >
I'm not adverse to making the gdt descriptors part of the per-cpu data. But I think your patch is missing some necessary changes to include/asm-i386/desc.h - what do you plan to do with the following definition there?
extern struct Xgt_desc_struct idt_descr, cpu_gdt_descr[NR_CPUS];
Also, it seems likely you may have broken APM and/or PnP BIOS.
>diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c >index cbc3206..d561a56 100644 >--- a/arch/i386/kernel/cpu/common.c >+++ b/arch/i386/kernel/cpu/common.c >@@ -4,6 +4,7 @@ > #include <linux/smp.h> > #include <linux/module.h> > #include <linux/percpu.h> >+#include <linux/bootmem.h> > #include <asm/semaphore.h> > #include <asm/processor.h> > #include <asm/i387.h> >@@ -18,6 +19,9 @@ > > #include "cpu.h" > >+DEFINE_PER_CPU(struct Xgt_desc_struct, cpu_gdt_descr); >+EXPORT_PER_CPU_SYMBOL(cpu_gdt_descr); >+ > DEFINE_PER_CPU(unsigned char, cpu_16bit_stack[CPU_16BIT_STACK_SIZE]); > EXPORT_PER_CPU_SYMBOL(cpu_16bit_stack); > >@@ -559,8 +563,9 @@ void __devinit cpu_init(void) > int cpu = smp_processor_id(); > struct tss_struct * t = &per_cpu(init_tss, cpu); > struct thread_struct *thread = ¤t->thread; >- struct desc_struct *gdt = get_cpu_gdt_table(cpu); >+ struct desc_struct *gdt; > __u32 stk16_off = (__u32)&per_cpu(cpu_16bit_stack, cpu); >+ struct Xgt_desc_struct *cpu_gdt_descr = &per_cpu(cpu_gdt_descr, cpu); > > if (cpu_test_and_set(cpu, cpu_initialized)) { > printk(KERN_WARNING "CPU#%d already initialized!\n", cpu); >@@ -577,6 +582,22 @@ void __devinit cpu_init(void) > set_in_cr4(X86_CR4_TSD); > } > >+ /* This is a horrible hack to allocate the GDT. The problem >+ * is that cpu_init() is called really early for the boot CPU >+ * (and hence needs bootmem) but much later for the secondary >+ * CPUs, when bootmem will have gone away */ >+ if (NODE_DATA(0)->bdata->node_bootmem_map) { >+ gdt = (struct desc_struct *)alloc_bootmem_pages(PAGE_SIZE); >+ /* alloc_bootmem_pages panics on failure, so no check */ >+ memset(gdt, 0, PAGE_SIZE); >+ } else { >+ gdt = (struct desc_struct *)get_zeroed_page(GFP_KERNEL); >+ if (unlikely(!gdt)) { >+ printk(KERN_CRIT "CPU%d failed to allocate GDT\n", cpu); >+ for (;;) local_irq_enable(); >+ } >+ } >+ > /* > * Initialize the per-CPU GDT with the boot GDT, > * and set up the GDT descriptor: > >
Can't you get rid of this ugly hack _and_ optimize the code at the same time? I don't understand the details of voyager bringup, but it seems clear that the BSP or node 0 is special in both sub-architectures. If it is special anyway, the conditional logic can be merged, and better yet, the allocation for the first caller of cpu_init() can skip the allocation entirely - it can simply use the boot GDT, which is already page-aligned and ready to go. This gets rid of the alloc_bootmem_pages() piece of the hack above.
Also, it seems you left the allocation of the GDT in do_boot_cpu(). How do you plan to make sure that GDT allocation is compatible with hotplug CPU startup? I was worried about that, which is why I moved the GDT allocation for secondary processors (originally in arch/i386/kernel/cpu/common.c) to smpboot.c.
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