Re: [PATCHv6 21/30] x86/acpi, x86/boot: Add multiprocessor wake-up support

Thomas Gleixner
2022-03-17T12:45:03Z

On Wed, Mar 16 2022 at 05:08, Kirill A. Shutemov wrote:
> +#ifdef CONFIG_X86_64
> +/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> +{
> + static physid_mask_t apic_id_wakemap = PHYSID_MASK_NONE;
> + u8 timeout;
> +
> + /* Remap mailbox memory only for the first call to acpi_wakeup_cpu() */
> + if (physids_empty(apic_id_wakemap)) {

I had to read this condition twice.

Why not checking (!acpi_mp_wake_mailbox)? Too obvious, right?

> + acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> + sizeof(*acpi_mp_wake_mailbox),
> + MEMREMAP_WB);
> + }
> +
> + /*
> + * According to the ACPI specification r6.4, section titled
> + * "Multiprocessor Wakeup Structure" the mailbox-based wakeup
> + * mechanism cannot be used more than once for the same CPU.
> + * Skip wakeups if they are attempted more than once.
> + */
> + if (physid_isset(apicid, apic_id_wakemap)) {
> + pr_err("CPU already awake (APIC ID %x), skipping wakeup\n",
> + apicid);
> + return -EINVAL;
> + }
> +
> + spin_lock(&mailbox_lock);

What is this lock actually protecting? Wakeup of secondary CPUs is fully
serialized in the core code already.

Thanks,

tglx