Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

[Usama Arif]

On 21/02/2023 23:18, David Woodhouse wrote:
> On Tue, 2023-02-21 at 22:41 +0100, Thomas Gleixner wrote:
> > @@ -57,6 +58,7 @@ asmlinkage acpi_status __visible x86_acp
> >    */
> >   int x86_acpi_suspend_lowlevel(void)
> >   {
> > +       unsigned int __maybe_unused saved_smpboot_ctrl;
> >          struct wakeup_header *header =
> >                  (struct wakeup_header *) __va(real_mode_header->wakeup_header);
> >   
> > @@ -115,7 +117,8 @@ int x86_acpi_suspend_lowlevel(void)
> >          early_gdt_descr.address =
> >                          (unsigned long)get_cpu_gdt_rw(smp_processor_id());
> >          initial_gs = per_cpu_offset(smp_processor_id());
> > -       smpboot_control = 0;
> > +       /* Force the startup into boot mode */
> > +       saved_smpboot_ctrl = xchg(&smpboot_control, 0);
> >   #endif
> >          initial_code = (unsigned long)wakeup_long64;
> >          saved_magic = 0x123456789abcdef0L;
> > @@ -128,6 +131,9 @@ int x86_acpi_suspend_lowlevel(void)
> >          pause_graph_tracing();
> >          do_suspend_lowlevel();
> >          unpause_graph_tracing();
> > +
> > +       if (IS_ENABLED(CONFIG_64BIT) && IS_ENABLED(CONFIG_SMP))
> > +               smpboot_control = saved_smpboot_ctrl;
> >          return 0;
> >   }
> >   
>
> But wait, why is this giving it a dedicated temp_stack anyway? Why
> can't it use that CPU's idle thread stack like we usually do? I already
> made idle_thread_get() accessible from here. So we could do this...
>
> @@ -111,14 +112,16 @@ int x86_acpi_suspend_lowlevel(void)
>          saved_magic = 0x12345678;
>   #else /* CONFIG_64BIT */
>   #ifdef CONFIG_SMP
> -       initial_stack = (unsigned long)temp_stack + sizeof(temp_stack);
> -       early_gdt_descr.address =
> -                       (unsigned long)get_cpu_gdt_rw(smp_processor_id());
> -       initial_gs = per_cpu_offset(smp_processor_id());
> -       smpboot_control = 0;
> +       if (!(smpboot_control & STARTUP_PARALLEL_MASK)) {
> +               unsigned int cpu = smp_processor_id();
> +               initial_stack = (unsigned long)idle_thread_get(cpu)->thread.sp;
> +               early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
> +               initial_gs = per_cpu_offset(cpu);
> +               smpboot_control = 0;
> +       }
>   #endif
>          initial_code = (unsigned long)wakeup_long64;
>
>
> But that's a whole bunch of pointless, because it can be even further
> simplified to just let the find its own crap like the secondaries do,
> except in the 'OMG CPUID won't tell me' case where it has to be told:
>
> So how about we just do something more like this. I'd *quite* like to
> put the actual handling of smpboot_control into a function we call in
> smpboot.c. and that whole x86_acpi_suspend_lowlevel() function wants
> all its horrid 64bit/smp ifdefs fixed up (and is there any reason
> there's a generic part saving CR0 and IA32_MISC_ENABLE right in the
> middle of some !CONFIG_64BIT parts? I don't see ordering constraints
> there). But this should work, I think:
>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 33c0d5fd8af6..72b9375fec7c 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -208,4 +208,6 @@ extern unsigned int smpboot_control;
>   #define STARTUP_APICID_CPUID_0B	0x40000000
>   #define STARTUP_APICID_CPUID_01	0x20000000
>   
> +#define STARTUP_PARALLEL_MASK	0x60000000
> +

Probably could define STARTUP_PARALLEL_MASK as STARTUP_APICID_CPUID_0B | 
STARTUP_APICID_CPUID_01 instead? otherwise if its a separate bit, it 
needs to be set in native_smp_prepare_cpus as well for this to work?

>   #endif /* _ASM_X86_SMP_H */
> diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
> index 06adf340a0f1..a1343a900caf 100644
> --- a/arch/x86/kernel/acpi/sleep.c
> +++ b/arch/x86/kernel/acpi/sleep.c
> @@ -16,17 +16,14 @@
>   #include <asm/cacheflush.h>
>   #include <asm/realmode.h>
>   #include <asm/hypervisor.h>
> -
> +#include <asm/smp.h>
> +#include <linux/smpboot.h>
>   #include <linux/ftrace.h>
>   #include "../../realmode/rm/wakeup.h"
>   #include "sleep.h"
>   
>   unsigned long acpi_realmode_flags;
>   
> -#if defined(CONFIG_SMP) && defined(CONFIG_64BIT)
> -static char temp_stack[4096];
> -#endif
> -
>   /**
>    * acpi_get_wakeup_address - provide physical address for S3 wakeup
>    *
> @@ -111,14 +108,11 @@ int x86_acpi_suspend_lowlevel(void)
>   	saved_magic = 0x12345678;
>   #else /* CONFIG_64BIT */
>   #ifdef CONFIG_SMP
> -	initial_stack = (unsigned long)temp_stack + sizeof(temp_stack);
> -	early_gdt_descr.address =
> -			(unsigned long)get_cpu_gdt_rw(smp_processor_id());
> -	initial_gs = per_cpu_offset(smp_processor_id());
> -	smpboot_control = 0;
> +	if (!(smpboot_control & STARTUP_PARALLEL_MASK))
> +		smpboot_control = STARTUP_SECONDARY | cpu_physical_id(smp_processor_id());
>   #endif
>   	initial_code = (unsigned long)wakeup_long64;
> -       saved_magic = 0x123456789abcdef0L;
> +	saved_magic = 0x123456789abcdef0L;
>   #endif /* CONFIG_64BIT */
>   
>   	/*