Date:   Mon, 24 May 2021 16:51:33 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     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>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/1] x86/acpi, x86/boot: Add multiprocessor wake-up support

On Monday, May 24, 2021 8:02:21 AM CEST Kuppuswamy Sathyanarayanan wrote:
> As per ACPI specification r6.4, sec 5.2.12.19, a new sub
> structure – multiprocessor wake-up structure - is added to the
> ACPI Multiple APIC Description Table (MADT) to describe the
> information of the mailbox. If a platform firmware produces the
> multiprocessor wake-up structure, then OS may use this new
> mailbox-based mechanism to wake up the APs.
> 
> Add ACPI MADT wake table parsing support for x86 platform and if
> MADT wake table is present, update apic->wakeup_secondary_cpu with
> new API which uses MADT wake mailbox to wake-up CPU.
> 
> Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> Reviewed-by: Andi Kleen <ak@...ux.intel.com>

It would help if you CCed this to linux-acpi@...r.kernel.org.

> ---
> 
> Changes since v4:
>  * Used smp_store_release() in place of WRITE_ONCE().
>  * Addressed some checkpatch warnings.
> 
> Changes since v3:
>  * Removed acpi_mp_wake_mailbox_init() and moved init code to
>    acpi_wakeup_cpu().
>  * Removed redundant NULL pointer check for acpi_mp_wake_mailbox.
>  * Added comments/debug prints as per Rafael's suggestion.
>  * Removed MADT/SVKL ACPI patches from this patchset. It will be
>    merged via ACPICA submission.
> 
>  arch/x86/include/asm/apic.h |  3 ++
>  arch/x86/kernel/acpi/boot.c | 96 +++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/apic/apic.c |  8 ++++
>  3 files changed, 107 insertions(+)
> 
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index 412b51e059c8..3e94e1f402ea 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -487,6 +487,9 @@ static inline unsigned int read_apic_id(void)
>  	return apic->get_apic_id(reg);
>  }
>  
> +typedef int (*wakeup_cpu_handler)(int apicid, unsigned long start_eip);
> +extern void acpi_wake_cpu_handler_update(wakeup_cpu_handler handler);
> +
>  extern int default_apic_id_valid(u32 apicid);
>  extern int default_acpi_madt_oem_check(char *, char *);
>  extern void default_setup_apic_routing(void);
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 14cd3186dc77..c51134eb55d0 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -65,6 +65,10 @@ int acpi_fix_pin2_polarity __initdata;
>  static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
>  #endif
>  
> +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
>  /*
>   * Locks related to IOAPIC hotplug
> @@ -329,6 +333,68 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
>  	return 0;
>  }
>  
> +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> +{
> +	u8 timeout = 0xFF;
> +
> +	/* Remap mailbox memory only for the first call to acpi_wakeup_cpu() */
> +	if (physids_empty(apic_id_wakemap)) {
> +		acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> +						sizeof(*acpi_mp_wake_mailbox),
> +						MEMREMAP_WB);
> +	}
> +
> +	/*
> +	 * According to the ACPI specification r6.4, sec 5.2.12.19, the
> +	 * mailbox-based wakeup mechanism cannot be used more than once
> +	 * for the same CPU, so skip sending wake commands to already
> +	 * awake CPU.
> +	 */
> +	if (physid_isset(apicid, apic_id_wakemap)) {
> +		pr_err("CPU already awake (APIC ID %x), skipping wakeup\n",
> +		       apicid);
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * Mailbox memory is shared between firmware and OS. Firmware will
> +	 * listen on mailbox command address, and once it receives the wakeup
> +	 * command, CPU associated with the given apicid will be booted. So,
> +	 * the value of apic_id and wakeup_vector has to be set before updating
> +	 * the wakeup command. So use smp_store_release to let the compiler know
> +	 * about it and preserve the order of writes.
> +	 */
> +	smp_store_release(&acpi_mp_wake_mailbox->apic_id, apicid);
> +	smp_store_release(&acpi_mp_wake_mailbox->wakeup_vector, start_ip);
> +	smp_store_release(&acpi_mp_wake_mailbox->command,
> +			  ACPI_MP_WAKE_COMMAND_WAKEUP);
> +
> +	/*
> +	 * After writing wakeup command, wait for maximum timeout of 0xFF
> +	 * for firmware to reset the command address back zero to indicate
> +	 * the successful reception of command.
> +	 * NOTE: 255 as timeout value is decided based on our experiments.
> +	 *
> +	 * XXX: Change the timeout once ACPI specification comes up with
> +	 *      standard maximum timeout value.
> +	 */
> +	while (READ_ONCE(acpi_mp_wake_mailbox->command) && timeout--)
> +		cpu_relax();
> +
> +	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;
> +}
> +
>  #endif				/*CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef CONFIG_X86_IO_APIC
> @@ -1086,6 +1152,30 @@ static int __init acpi_parse_madt_lapic_entries(void)
>  	}
>  	return 0;
>  }
> +
> +static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> +				      const unsigned long end)
> +{
> +	struct acpi_madt_multiproc_wakeup *mp_wake;
> +
> +	if (acpi_mp_wake_mailbox)
> +		return -EINVAL;
> +
> +	if (!IS_ENABLED(CONFIG_SMP))
> +		return -ENODEV;
> +
> +	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> +	if (BAD_MADT_ENTRY(mp_wake, end))
> +		return -EINVAL;
> +
> +	acpi_table_print_madt_entry(&header->common);
> +
> +	acpi_mp_wake_mailbox_paddr = mp_wake->base_address;
> +
> +	acpi_wake_cpu_handler_update(acpi_wakeup_cpu);
> +
> +	return 0;
> +}
>  #endif				/* CONFIG_X86_LOCAL_APIC */
>  
>  #ifdef	CONFIG_X86_IO_APIC
> @@ -1284,6 +1374,12 @@ static void __init acpi_process_madt(void)
>  
>  				smp_found_config = 1;
>  			}
> +
> +			/*
> +			 * Parse MADT MP Wake entry.
> +			 */
> +			acpi_table_parse_madt(ACPI_MADT_TYPE_MULTIPROC_WAKEUP,
> +					      acpi_parse_mp_wake, 1);
>  		}
>  		if (error == -EINVAL) {
>  			/*
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 4f26700f314d..f1b90a4b89e8 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2554,6 +2554,14 @@ u32 x86_msi_msg_get_destid(struct msi_msg *msg, bool extid)
>  }
>  EXPORT_SYMBOL_GPL(x86_msi_msg_get_destid);
>  
> +void __init acpi_wake_cpu_handler_update(wakeup_cpu_handler handler)
> +{
> +	struct apic **drv;
> +
> +	for (drv = __apicdrivers; drv < __apicdrivers_end; drv++)
> +		(*drv)->wakeup_secondary_cpu = handler;
> +}
> +
>  /*
>   * Override the generic EOI implementation with an optimized version.
>   * Only called during early boot when only one CPU is active and with
> 

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