linux-kernel - Re: [PATCH v3 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up support

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Date:   Mon, 10 May 2021 14:15:29 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>
Cc:     Rafael J Wysocki <rjw@...ysocki.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v3 3/3] x86/acpi, x86/boot: Add multiprocessor wake-up
 support



On 5/10/21 10:24 AM, Rafael J. Wysocki wrote:
> The wakeup function can return an error when it is called for the
> second time on the same CPU.

To do this, we can only maintain the wakeup status of the CPUs. Can
you check whether following physid_mask based status maintenance is
acceptable?

--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -67,6 +67,7 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;

  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
  static u64 acpi_mp_wake_mailbox_paddr;
+static physid_mask_t apic_id_wakemap = PHYSID_MASK_NONE;

  #ifdef CONFIG_X86_IO_APIC
  /*
@@ -347,6 +348,13 @@ static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)

         acpi_mp_wake_mailbox_init();

+       /* Check if the given CPU (apicid) is already awake */
+       if (physid_isset(apicid, apic_id_wakemap)) {
+               pr_err("APIC ID %x is already awake, so failed to wakeup\n",
+                               apicid);
+               return -EINVAL;
+       }
+
         if (!acpi_mp_wake_mailbox)
                 return -EINVAL;

@@ -374,8 +382,18 @@ static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
         while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
                 cpu_relax();

-       /* If timedout, return error */
-       return timeout ? 0 : -EIO;
+       if (timeout) {
+               /*
+                * If the CPU wakeup process is successful, store the
+                * status in apic_id_wakemap to prevent re-wakeup
+                * requests.
+                */
+               physid_set(apicid, apic_id_wakemap);
+               return 0;
+       }
+
+       /* If timed out (timeout == 0), return error */
+       return -EIO;
  }


-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer