linux-kernel - Re: [PATCH v9 0/8] Parallel CPU bringup for x86

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Message-ID: <87356yofw3.ffs@tglx>
Date:   Tue, 21 Feb 2023 22:41:32 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw2@...radead.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:     Kim Phillips <kim.phillips@....com>,
        Usama Arif <usama.arif@...edance.com>, arjan@...ux.intel.com,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, x86@...nel.org, pbonzini@...hat.com,
        paulmck@...nel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, rcu@...r.kernel.org, mimoja@...oja.de,
        hewenliang4@...wei.com, thomas.lendacky@....com, seanjc@...gle.com,
        pmenzel@...gen.mpg.de, fam.zheng@...edance.com,
        punit.agrawal@...edance.com, simon.evans@...edance.com,
        liangma@...ngbit.com,
        "Limonciello, Mario" <Mario.Limonciello@....com>,
        Piotr Gorski <piotrgorski@...hyos.org>
Subject: Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

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 (Usama, I think my tree is fairly out of date now so I'll let you do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