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Subject[PATCH 14/26] x86/acpi, x86/boot: Add multiprocessor wake-up support
Date
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

TDX cannot use INIT/SIPI protocol to bring up secondary CPUs because it
requires assistance from untrusted VMM.

For platforms that do not support SIPI/INIT, ACPI defines a wakeup
model (using mailbox) via MADT multiprocessor wakeup structure. More
details about it can be found in ACPI specification v6.4, the section
titled "Multiprocessor Wakeup Structure". If a platform firmware
produces the multiprocessor wakeup structure, then OS may use this
new mailbox-based mechanism to wake up the APs.

Add ACPI MADT wake structure parsing support for x86 platform and if
MADT wake table is present, update apic->wakeup_secondary_cpu_64 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>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/apic.h | 5 ++
arch/x86/kernel/acpi/boot.c | 114 ++++++++++++++++++++++++++++++++++++
arch/x86/kernel/apic/apic.c | 10 ++++
3 files changed, 129 insertions(+)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index 35006e151774..bd8ae0a7010a 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -490,6 +490,11 @@ static inline unsigned int read_apic_id(void)
return apic->get_apic_id(reg);
}

+#ifdef CONFIG_X86_64
+typedef int (*wakeup_cpu_handler)(int apicid, unsigned long start_eip);
+extern void acpi_wake_cpu_handler_update(wakeup_cpu_handler handler);
+#endif
+
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 5b6d1a95776f..af204a217575 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -65,6 +65,15 @@ static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE;
static bool acpi_support_online_capable;
#endif

+#ifdef CONFIG_X86_64
+/* Physical address of the Multiprocessor Wakeup Structure mailbox */
+static u64 acpi_mp_wake_mailbox_paddr;
+/* Virtual address of the Multiprocessor Wakeup Structure mailbox */
+static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
+/* Lock to protect mailbox (acpi_mp_wake_mailbox) from parallel access */
+static DEFINE_SPINLOCK(mailbox_lock);
+#endif
+
#ifdef CONFIG_X86_IO_APIC
/*
* Locks related to IOAPIC hotplug
@@ -336,6 +345,80 @@ acpi_parse_lapic_nmi(union acpi_subtable_headers * header, const unsigned long e
return 0;
}

+#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;
+ unsigned long flags;
+ u8 timeout;
+
+ /* 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, 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_irqsave(&mailbox_lock, flags);
+
+ /*
+ * 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.
+ *
+ * The value of apic_id and wakeup_vector has to be set before updating
+ * the wakeup command. To let compiler preserve order of writes, use
+ * smp_store_release.
+ */
+ 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 the 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: 0xFF as timeout value is decided based on our experiments.
+ *
+ * XXX: Change the timeout once ACPI specification comes up with
+ * standard maximum timeout value.
+ */
+ timeout = 0xFF;
+ while (READ_ONCE(acpi_mp_wake_mailbox->command) && --timeout)
+ cpu_relax();
+
+ /* If timed out (timeout == 0), return error */
+ if (!timeout) {
+ spin_unlock_irqrestore(&mailbox_lock, flags);
+ return -EIO;
+ }
+
+ /*
+ * 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);
+
+ spin_unlock_irqrestore(&mailbox_lock, flags);
+
+ return 0;
+}
+#endif
#endif /*CONFIG_X86_LOCAL_APIC */

#ifdef CONFIG_X86_IO_APIC
@@ -1083,6 +1166,29 @@ static int __init acpi_parse_madt_lapic_entries(void)
}
return 0;
}
+
+#ifdef CONFIG_X86_64
+static int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
+ const unsigned long end)
+{
+ struct acpi_madt_multiproc_wakeup *mp_wake;
+
+ 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_64 */
#endif /* CONFIG_X86_LOCAL_APIC */

#ifdef CONFIG_X86_IO_APIC
@@ -1278,6 +1384,14 @@ static void __init acpi_process_madt(void)

smp_found_config = 1;
}
+
+#ifdef CONFIG_X86_64
+ /*
+ * Parse MADT MP Wake entry.
+ */
+ acpi_table_parse_madt(ACPI_MADT_TYPE_MULTIPROC_WAKEUP,
+ acpi_parse_mp_wake, 1);
+#endif
}
if (error == -EINVAL) {
/*
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b70344bf6600..3c8f2c797a98 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2551,6 +2551,16 @@ u32 x86_msi_msg_get_destid(struct msi_msg *msg, bool extid)
}
EXPORT_SYMBOL_GPL(x86_msi_msg_get_destid);

+#ifdef CONFIG_X86_64
+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_64 = handler;
+}
+#endif
+
/*
* Override the generic EOI implementation with an optimized version.
* Only called during early boot when only one CPU is active and with
--
2.32.0
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