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    SubjectRe: [PATCH v12 06/11] x86/smpboot: Remove initial_stack on 64-bit
    Date
    On Sun, Feb 26 2023 at 11:07, Usama Arif wrote:
    > From: Brian Gerst <brgerst@gmail.com>
    >
    > Eliminating global variables from the CPU startup path in order to simplify
    > it and facilitate parallel startup.

    As this patch is now part of the parallel boot series and actually
    introduces smpboot_control, the above is neither accurate nor useful.

    Folks, really.

    > Remove initial_stack, and load RSP from current_task->thread.sp instead.


    > #ifdef CONFIG_SMP
    > - initial_stack = (unsigned long)temp_stack + sizeof(temp_stack);
    > + current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack);

    This lacks a comment about the temporary (ab)use of current->thread.sp

    > early_gdt_descr.address =
    > (unsigned long)get_cpu_gdt_rw(smp_processor_id());
    > initial_gs = per_cpu_offset(smp_processor_id());
    > + smpboot_control = smp_processor_id();
    > #endif

    > @@ -241,6 +241,24 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
    > UNWIND_HINT_EMPTY
    > ANNOTATE_NOENDBR // above
    >
    > +#ifdef CONFIG_SMP
    > + movl smpboot_control(%rip), %ecx
    > +
    > + /* Get the per cpu offset for the given CPU# which is in ECX */
    > + movq __per_cpu_offset(,%rcx,8), %rdx
    > +#else
    > + xorl %edx, %edx
    > +#endif /* CONFIG_SMP */

    Sigh, we should finally make CONFIG_SMP def_bool y ...

    > + /*
    > + * Setup a boot time stack - Any secondary CPU will have lost its stack
    > + * by now because the cr3-switch above unmaps the real-mode stack.
    > + *
    > + * RDX contains the per-cpu offset
    > + */
    > + movq pcpu_hot + X86_current_task(%rdx), %rax
    > + movq TASK_threadsp(%rax), %rsp
    > +
    > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
    > index b18c1385e181..62e3bf37f0b8 100644
    > --- a/arch/x86/kernel/smpboot.c
    > +++ b/arch/x86/kernel/smpboot.c
    > @@ -1112,7 +1112,12 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
    > idle->thread.sp = (unsigned long)task_pt_regs(idle);
    > early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
    > initial_code = (unsigned long)start_secondary;
    > - initial_stack = idle->thread.sp;
    > +
    > + if (IS_ENABLED(CONFIG_X86_32)) {
    > + initial_stack = idle->thread.sp;
    > + } else {
    > + smpboot_control = cpu;
    > + }

    Please remove the pointless brackets.

    Thanks,

    tglx

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