[PATCH v3 0/3] Add multiprocessor wake-up support

[PATCH v3 0/3] Add multiprocessor wake-up support

[Kuppuswamy Sathyanarayanan]

Add multiprocessor wakeup support using MADT ACPI table for x86
platforms. It uses mailbox based mechanism to wake up the APs. You
can get more details about the ACPI table and mailbox protocol in
Guest-Host-Communication Interface (GHCI) for Intel Trust Domain
Extensions (Intel TDX) specification document (sec 4.1)

https://software.intel.com/content/dam/develop/external/us/en/documents/intel-tdx-guest-hypervisor-communication-interface.pdf

Changes since v2:
 * Moved acpi_wake_cpu_handler_update() definition to
   arch/x86/kernel/apic/apic.c
 * Added comments for WRITE_ONCE() usage.
 * Added error handling support to prevent re-trigger of
   acpi_wakeup_cpu() and to detect the failure case.

Changes since v1:
 * Removed signoff from Rob and Erik.

Kuppuswamy Sathyanarayanan (3):
  ACPICA: ACPI 6.4: MADT: add Multiprocessor Wakeup Mailbox Structure
  ACPI/table: Print MADT Wake table information
  x86/acpi, x86/boot: Add multiprocessor wake-up support

 arch/x86/include/asm/apic.h |  3 ++
 arch/x86/kernel/acpi/boot.c | 79 +++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/apic/apic.c |  8 ++++
 drivers/acpi/tables.c       | 11 ++++++
 include/acpi/actbl2.h       | 14 +++++++
 5 files changed, 115 insertions(+)

-- 
2.25.1

[PATCH v3 1/3] ACPICA: ACPI 6.4: MADT: add Multiprocessor Wakeup Mailbox Structure

[Kuppuswamy Sathyanarayanan]

ACPICA commit f1ee04207a212f6c519441e7e25397649ebc4cea

Add Multiprocessor Wakeup Mailbox Structure definition. It is useful
in parsing MADT Wake table.

Link: https://github.com/acpica/acpica/commit/f1ee0420
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 include/acpi/actbl2.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/acpi/actbl2.h b/include/acpi/actbl2.h
index b2362600b9ff..7dce422f6119 100644
--- a/include/acpi/actbl2.h
+++ b/include/acpi/actbl2.h
@@ -733,6 +733,20 @@ struct acpi_madt_multiproc_wakeup {
 	u64 base_address;
 };
 
+#define ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE	2032
+#define ACPI_MULTIPROC_WAKEUP_MB_FIRMWARE_SIZE	2048
+
+struct acpi_madt_multiproc_wakeup_mailbox {
+	u16 command;
+	u16 reserved;		/* reserved - must be zero */
+	u32 apic_id;
+	u64 wakeup_vector;
+	u8 reserved_os[ACPI_MULTIPROC_WAKEUP_MB_OS_SIZE];	/* reserved for OS use */
+	u8 reserved_firmware[ACPI_MULTIPROC_WAKEUP_MB_FIRMWARE_SIZE];	/* reserved for firmware use */
+};
+
+#define ACPI_MP_WAKE_COMMAND_WAKEUP    1
+
 /*
  * Common flags fields for MADT subtables
  */
-- 
2.25.1

[PATCH v3 2/3] ACPI/table: Print MADT Wake table information

[Kuppuswamy Sathyanarayanan]

When MADT is parsed, print MADT Wake table information as
debug message. It will be useful to debug CPU boot issues
related to MADT wake table.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
 drivers/acpi/tables.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 9d581045acff..206df4ad8b2b 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -207,6 +207,17 @@ void acpi_table_print_madt_entry(struct acpi_subtable_header *header)
 		}
 		break;
 
+	case ACPI_MADT_TYPE_MULTIPROC_WAKEUP:
+		{
+			struct acpi_madt_multiproc_wakeup *p;
+
+			p = (struct acpi_madt_multiproc_wakeup *) header;
+
+			pr_debug("MP Wake (Mailbox version[%d] base_address[%llx])\n",
+				 p->mailbox_version, p->base_address);
+		}
+		break;
+
 	default:
 		pr_warn("Found unsupported MADT entry (type = 0x%x)\n",
 			header->type);
-- 
2.25.1

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

[Kuppuswamy Sathyanarayanan]

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@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/include/asm/apic.h |  3 ++
 arch/x86/kernel/acpi/boot.c | 79 +++++++++++++++++++++++++++++++++++++
 arch/x86/kernel/apic/apic.c |  8 ++++
 3 files changed, 90 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..fce2aa7d718f 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -65,6 +65,9 @@ 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;
+
 #ifdef CONFIG_X86_IO_APIC
 /*
  * Locks related to IOAPIC hotplug
@@ -329,6 +332,52 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
 	return 0;
 }
 
+static void acpi_mp_wake_mailbox_init(void)
+{
+	if (acpi_mp_wake_mailbox)
+		return;
+
+	acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
+			sizeof(*acpi_mp_wake_mailbox), MEMREMAP_WB);
+}
+
+static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
+{
+	u8 timeout = 0xFF;
+
+	acpi_mp_wake_mailbox_init();
+
+	if (!acpi_mp_wake_mailbox)
+		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 WRITE_ONCE to let the compiler know about
+	 * it and preserve the order of writes.
+	 */
+	WRITE_ONCE(acpi_mp_wake_mailbox->apic_id, apicid);
+	WRITE_ONCE(acpi_mp_wake_mailbox->wakeup_vector, start_ip);
+	WRITE_ONCE(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 timedout, return error */
+	return timeout ? 0 : -EIO;
+}
+
 #endif				/*CONFIG_X86_LOCAL_APIC */
 
 #ifdef CONFIG_X86_IO_APIC
@@ -1086,6 +1135,30 @@ 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 +1357,12 @@ 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
-- 
2.25.1

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

[Kuppuswamy, Sathyanarayanan]

Hi Rafael/Thomas,

On 4/25/21 7:39 PM, 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.

Gentle ping. Any comments on this patch? I think I have addressed
the concerns raised by you in previous version.

> 
> Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> ---
>   arch/x86/include/asm/apic.h |  3 ++
>   arch/x86/kernel/acpi/boot.c | 79 +++++++++++++++++++++++++++++++++++++
>   arch/x86/kernel/apic/apic.c |  8 ++++
>   3 files changed, 90 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..fce2aa7d718f 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -65,6 +65,9 @@ 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;
> +
>   #ifdef CONFIG_X86_IO_APIC
>   /*
>    * Locks related to IOAPIC hotplug
> @@ -329,6 +332,52 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
>   	return 0;
>   }
>   
> +static void acpi_mp_wake_mailbox_init(void)
> +{
> +	if (acpi_mp_wake_mailbox)
> +		return;
> +
> +	acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> +			sizeof(*acpi_mp_wake_mailbox), MEMREMAP_WB);
> +}
> +
> +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> +{
> +	u8 timeout = 0xFF;
> +
> +	acpi_mp_wake_mailbox_init();
> +
> +	if (!acpi_mp_wake_mailbox)
> +		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 WRITE_ONCE to let the compiler know about
> +	 * it and preserve the order of writes.
> +	 */
> +	WRITE_ONCE(acpi_mp_wake_mailbox->apic_id, apicid);
> +	WRITE_ONCE(acpi_mp_wake_mailbox->wakeup_vector, start_ip);
> +	WRITE_ONCE(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 timedout, return error */
> +	return timeout ? 0 : -EIO;
> +}
> +
>   #endif				/*CONFIG_X86_LOCAL_APIC */
>   
>   #ifdef CONFIG_X86_IO_APIC
> @@ -1086,6 +1135,30 @@ 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 +1357,12 @@ 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
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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

[Rafael J. Wysocki]

On Mon, May 10, 2021 at 6:33 PM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
> Hi Rafael/Thomas,
>
> On 4/25/21 7:39 PM, 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.
>
> Gentle ping. Any comments on this patch? I think I have addressed
> the concerns raised by you in previous version.
>
> >
> > Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > Reviewed-by: Andi Kleen <ak@linux.intel.com>
> > ---
> >   arch/x86/include/asm/apic.h |  3 ++
> >   arch/x86/kernel/acpi/boot.c | 79 +++++++++++++++++++++++++++++++++++++
> >   arch/x86/kernel/apic/apic.c |  8 ++++
> >   3 files changed, 90 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..fce2aa7d718f 100644
> > --- a/arch/x86/kernel/acpi/boot.c
> > +++ b/arch/x86/kernel/acpi/boot.c
> > @@ -65,6 +65,9 @@ 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;
> > +
> >   #ifdef CONFIG_X86_IO_APIC
> >   /*
> >    * Locks related to IOAPIC hotplug
> > @@ -329,6 +332,52 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
> >       return 0;
> >   }
> >
> > +static void acpi_mp_wake_mailbox_init(void)
> > +{
> > +     if (acpi_mp_wake_mailbox)
> > +             return;
> > +
> > +     acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> > +                     sizeof(*acpi_mp_wake_mailbox), MEMREMAP_WB);
> > +}
> > +
> > +static int acpi_wakeup_cpu(int apicid, unsigned long start_ip)
> > +{
> > +     u8 timeout = 0xFF;
> > +
> > +     acpi_mp_wake_mailbox_init();
> > +
> > +     if (!acpi_mp_wake_mailbox)
> > +             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 WRITE_ONCE to let the compiler know about
> > +      * it and preserve the order of writes.
> > +      */
> > +     WRITE_ONCE(acpi_mp_wake_mailbox->apic_id, apicid);
> > +     WRITE_ONCE(acpi_mp_wake_mailbox->wakeup_vector, start_ip);
> > +     WRITE_ONCE(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 timedout, return error */
> > +     return timeout ? 0 : -EIO;

I'm not sure how my comment regarding the fact that for a given CPU
this function is only usable once has been addressed.

While it may not be a practical concern in the use case that you are
after (TDX), this is a generic mechanism and it needs to cover other
possible usage scenarios.

> > +}
> > +
> >   #endif                              /*CONFIG_X86_LOCAL_APIC */
> >
> >   #ifdef CONFIG_X86_IO_APIC
> > @@ -1086,6 +1135,30 @@ 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 +1357,12 @@ 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
> >
>
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer

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

[Kuppuswamy, Sathyanarayanan]

On 5/10/21 9:55 AM, Rafael J. Wysocki wrote:
> I'm not sure how my comment regarding the fact that for a given CPU
> this function is only usable once has been addressed.
> 
> While it may not be a practical concern in the use case that you are
> after (TDX), this is a generic mechanism and it needs to cover other
> possible usage scenarios.

For the same CPU, if we try to use mailbox again, firmware will not
respond to it. So the command will timeout and return error.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

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

[Andi Kleen]

On Mon, May 10, 2021 at 10:10:24AM -0700, Kuppuswamy, Sathyanarayanan wrote:
> 
> 
> On 5/10/21 9:55 AM, Rafael J. Wysocki wrote:
> > I'm not sure how my comment regarding the fact that for a given CPU
> > this function is only usable once has been addressed.
> > 
> > While it may not be a practical concern in the use case that you are
> > after (TDX), this is a generic mechanism and it needs to cover other
> > possible usage scenarios.
> 
> For the same CPU, if we try to use mailbox again, firmware will not
> respond to it. So the command will timeout and return error.

Right because the firmware code doesn't run anymore.

The only possibility would be for Linux to put back some code that spins
and waits again, but that would be quite pointless and wasteful.

-Andi

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

[Rafael J. Wysocki]

On Mon, May 10, 2021 at 7:22 PM Andi Kleen <ak@linux.intel.com> wrote:
>
> On Mon, May 10, 2021 at 10:10:24AM -0700, Kuppuswamy, Sathyanarayanan wrote:
> >
> >
> > On 5/10/21 9:55 AM, Rafael J. Wysocki wrote:
> > > I'm not sure how my comment regarding the fact that for a given CPU
> > > this function is only usable once has been addressed.
> > >
> > > While it may not be a practical concern in the use case that you are
> > > after (TDX), this is a generic mechanism and it needs to cover other
> > > possible usage scenarios.
> >
> > For the same CPU, if we try to use mailbox again, firmware will not
> > respond to it. So the command will timeout and return error.
>
> Right because the firmware code doesn't run anymore.
>
> The only possibility would be for Linux to put back some code that spins
> and waits again, but that would be quite pointless and wasteful.

The wakeup function can return an error when it is called for the
second time on the same CPU.

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

[Kuppuswamy, Sathyanarayanan]

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

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

[Rafael J. Wysocki]

On Mon, May 10, 2021 at 11:15 PM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
>
>
> 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?

It would work for me except for a couple of nits below.

> --- 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 */

The reason why is that the wakeup mechanism used here is only usable
once per CPU by the spec, so I would add this information to the
comment.  Maybe something like "According to the ACPI specification
(ACPI 6.4, Section ...), the mailbox-based wakeup mechanism cannot be
used more than once for the same CPU, so avoid doing that."

> +       if (physid_isset(apicid, apic_id_wakemap)) {
> +               pr_err("APIC ID %x is already awake, so failed to wakeup\n",
> +                               apicid);

And I would reword the message like this "CPU already awake (APIC ID
%x), skipping wakeup\n".

> +               return -EINVAL;
> +       }
> +
>          if (!acpi_mp_wake_mailbox)

Note, though, that instead of having this additional flag, you may as
well create a mask that is fully populated initially and clear the IDs
of the woken-up CPUs in it.  Then, you'd only need one check here
instead of two.

>                  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

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

[Rafael J. Wysocki]

On Mon, May 10, 2021 at 7:10 PM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
>
>
> On 5/10/21 9:55 AM, Rafael J. Wysocki wrote:
> > I'm not sure how my comment regarding the fact that for a given CPU
> > this function is only usable once has been addressed.
> >
> > While it may not be a practical concern in the use case that you are
> > after (TDX), this is a generic mechanism and it needs to cover other
> > possible usage scenarios.
>
> For the same CPU, if we try to use mailbox again, firmware will not
> respond to it.

Well, theoretically, but what if it checks the mailbox every time for
all CPUs?  Or similar?

> So the command will timeout and return error.

If the firmware behaves as expected, but what if it doesn't?