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SubjectRe: [PATCH v9 0/8] Parallel CPU bringup for x86_64
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David!

On Tue, Feb 21 2023 at 19:10, David Woodhouse wrote:
> On Tue, 2023-02-21 at 13:14 +0100, Oleksandr Natalenko wrote:
> (Usama, I think my tree is fairly out of date now so I'll let you do
> that? Thanks!).
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 50621793671d..3db77a257ae2 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1571,6 +1571,17 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
>
> void arch_thaw_secondary_cpus_begin(void)
> {
> + /*
> + * On suspend, smpboot_control will have been zeroed to allow the
> + * boot CPU to use explicitly passed values including a temporary
> + * stack. Since native_smp_prepare_cpus() won't be called again,
> + * restore the appropriate value for the parallel startup modes.
> + */
> + if (do_parallel_bringup) {
> + smpboot_control = STARTUP_SECONDARY |
> + (x2apic_mode ? STARTUP_APICID_CPUID_0B : STARTUP_APICID_CPUID_01);
> + }

My bad taste sensor reports: "Out of effective range"

Why on earth can't you fix the wreckage exactly where it happens,
i.e. in x86_acpi_suspend_lowlevel() ?

--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -16,6 +16,7 @@
#include <asm/cacheflush.h>
#include <asm/realmode.h>
#include <asm/hypervisor.h>
+#include <asm/smp.h>

#include <linux/ftrace.h>
#include "../../realmode/rm/wakeup.h"
@@ -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;
}

That's too bloody obvious, too self explaining, not enough duplicated
code and does not need any fixups when the smpboot_control bits are
changed later, right?

Thanks,

tglx

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