On 06/04/2018 10:24 PM, Chang S. Bae wrote:
> The CPU (and node) number will be written, as early enough,
> to the segment limit of per CPU data and TSC_AUX MSR entry.
> The information has been retrieved by vgetcpu in user space
> and will be also loaded from the paranoid entry, when
> FSGSBASE enabled. So, it is moved out from vDSO to the CPU
> initialization path where IST setup is serialized.
>
> Now, redundant setting of the segment in entry/vdso/vma.c
> was removed; a substantial code removal. It removes a
> hotplug notifier, makes a facility useful to both the kernel
> and userspace unconditionally available much sooner, and
> unification with i386. (Thanks to HPA for suggesting the
> cleanup)
>
> Signed-off-by: Chang S. Bae <chang.seok....@intel.com>
> Cc: H. Peter Anvin <h...@zytor.com>
> Cc: Dave Hansen <dave.han...@linux.intel.com>
> Cc: Andy Lutomirski <l...@kernel.org>
> Cc: Andi Kleen <a...@linux.intel.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@kernel.org>
> ---
> 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.
-Mika
>
> void __init setup_per_cpu_areas(void)
>
