Messages in this thread | | | Subject | Re: [PATCH 6/6] x86/vdso: Move out the CPU number store | From | Mika Penttilä <> | Date | Tue, 5 Jun 2018 08:19:43 +0300 |
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On 06/05/2018 07:44 AM, Bae, Chang Seok wrote: >>> diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c >>> index ea554f8..e716e94 100644 >>> --- a/arch/x86/kernel/setup_percpu.c >>> +++ b/arch/x86/kernel/setup_percpu.c >>> @@ -155,12 +155,21 @@ static void __init pcpup_populate_pte(unsigned long addr) >>> >>> static inline void setup_percpu_segment(int cpu) >>> { >>> -#ifdef CONFIG_X86_32 >>> - struct desc_struct d = GDT_ENTRY_INIT(0x8092, per_cpu_offset(cpu), >>> - 0xFFFFF); >>> +#ifdef CONFIG_NUMA >>> + unsigned long node = early_cpu_to_node(cpu); >>> +#else >>> + unsigned long node = 0; >>> +#endif >>> + struct desc_struct d = GDT_ENTRY_INIT(0x0, per_cpu_offset(cpu), >>> + make_lsl_tscp(cpu, node)); >>> + >>> + d.type = 5; /* R0 data, expand down, accessed */ >>> + d.dpl = 3; /* Visible to user code */ >>> + d.s = 1; /* Not a system segment */ >>> + d.p = 1; /* Present */ >>> + d.d = 1; /* 32-bit */ >>> >>> write_gdt_entry(get_cpu_gdt_rw(cpu), GDT_ENTRY_PERCPU, &d, DESCTYPE_S); >>> -#endif >>> } > >> This won't work on X86-32 because it actually uses the segment limit with fs: access. So there >> is a reason why the lsl based method is X86-64 only. > > The limit will be consumed in X86-64 only, while the unification with i386 was suggested for a > different reason. > > Thanks, > Chang >
The unification affects i386, and the limit is consumed by the processor with fs: access. The limit was 0xFFFFF before, now it depends on the cpu/node. So accesses on small number cpus are likely to fault.
--Mika
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