On Thu, 2023-02-09 at 10:19 +0000, Usama Arif wrote:
>
>
> On 09/02/2023 10:06, David Woodhouse wrote:
> > On Thu, 2023-02-09 at 09:49 +0000, Usama Arif wrote:
> > >
> > > --- a/arch/x86/kernel/smpboot.c
> > > +++ b/arch/x86/kernel/smpboot.c
> > > @@ -1080,6 +1080,7 @@ wakeup_cpu_via_init_nmi(int cpu, unsigned long
> > > start_ip, int apicid,
> > > wakeup_cpu0_nmi, 0, "wake_cpu0");
> > >
> > > if (!boot_error) {
> > > + initial_gs = per_cpu_offset(cpu);
> >
> > That's for 64-bit.
> >
> > > enable_start_cpu0 = 1;
> > > *cpu0_nmi_registered = 1;
> > > id = apic->dest_mode_logical ? cpu0_logical_apicid :
> > > apicid;
> > > @@ -1188,10 +1189,14 @@ static int do_boot_cpu(int apicid, int cpu,
> > > struct task_struct *idle,
> > > boot_error = apic->wakeup_secondary_cpu_64(apicid,
> > > start_ip);
> > > else if (apic->wakeup_secondary_cpu)
> > > boot_error = apic->wakeup_secondary_cpu(apicid, start_ip);
> > > - else
> > > + else {
> > > + if(!cpu) {
> > > + early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
> > > + initial_stack = idle->thread.sp;
> > > + }
> >
> > And that's 32-bit.
> >
> > These were previously done in common_cpu_up() or do_boot_cpu(), which
> > means they were done not only for the wakeup_cpu_via_init_nmi() code
> > path, but also when we call apic->wakeup_secondary_cpu() (or _64()) for
> > the esoteric UV/NumaConnect machines.
> >
> > Thanks for diagnosing it so quickly; I'll work up a subtly different
> > fix.
> >
>
> Yeah, was just a hacky fix while I was trying to figure out the issue.
>
> do_boot_cpu is only called in cpu0 in hotplug case, so I think this a
> much better diff:
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 3ec5182d9698..f7ae82969ee4 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1136,13 +1136,16 @@ static int do_boot_cpu(int apicid, int cpu,
> struct task_struct *idle,
> idle->thread.sp = (unsigned long)task_pt_regs(idle);
> initial_code = (unsigned long)start_secondary;
>
> - if (IS_ENABLED(CONFIG_X86_32)) {
> + if (IS_ENABLED(CONFIG_X86_32) || !cpu) {
> early_gdt_descr.address = (unsigned
> long)get_cpu_gdt_rw(cpu);
> initial_stack = idle->thread.sp;
> } else if (!do_parallel_bringup) {
> smpboot_control = STARTUP_SECONDARY | apicid;
> }
>
> + if (!cpu)
> + initial_gs = per_cpu_offset(cpu);
> +
> /* Enable the espfix hack for this CPU */
> init_espfix_ap(cpu);
>
>
>
> > > boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
> > > cpu0_nmi_registered);
> > > -
> > > + }
> > > return boot_error;
> > > }
> > >
> >
I'm trying to find the actual startup path that CPU0 takes when woken
by an NMI.
Can't we make it take the secondary_startup_64 path that actually
checks smpboot_control, sees the STARTUP_SECONDARY flag set, and then
gets all these things from the per-cpu data as $DEITY (well, Thomas)
intended?
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