ACPI MADT doesn't allow to offline CPU after it got woke up. It limits
kexec: the second kernel won't be able to use more than one CPU.
Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
The acpi_wakeup_cpu() will use it to bring up secondary cpus.
Zero out mailbox address in the ACPI MADT wakeup structure to indicate
that the mailbox is not usable. This prevents the kexec()-ed kernel
from reading a vaild mailbox, which in turn makes the kexec()-ed kernel
only be able to use the boot CPU.
This is Linux-specific protocol and not reflected in ACPI spec.
Booting the second kernel with signle CPU is enough to cover the most
common case for kexec -- kdump.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
---
arch/x86/kernel/acpi/madt_wakeup.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 386adbb03094..5d92d12f1042 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -13,6 +13,11 @@ static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox __ro_afte
static int acpi_wakeup_cpu(u32 apicid, unsigned long start_ip)
{
+ if (!acpi_mp_wake_mailbox_paddr) {
+ pr_warn_once("No MADT mailbox: cannot bringup secondary CPUs. Booting with kexec?\n");
+ return -EOPNOTSUPP;
+ }
+
/*
* Remap mailbox memory only for the first call to acpi_wakeup_cpu().
*
@@ -78,6 +83,23 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
cpu_hotplug_disable_offlining();
+ /*
+ * ACPI MADT doesn't allow to offline CPU after it got woke up.
+ * It limits kexec: the second kernel won't be able to use more than
+ * one CPU.
+ *
+ * Now acpi_mp_wake_mailbox_paddr already has the mailbox address.
+ * The acpi_wakeup_cpu() will use it to bring up secondary cpus.
+ *
+ * Zero out mailbox address in the ACPI MADT wakeup structure to
+ * indicate that the mailbox is not usable. This prevents the
+ * kexec()-ed kernel from reading a vaild mailbox, which in turn
+ * makes the kexec()-ed kernel only be able to use the boot CPU.
+ *
+ * This is Linux-specific protocol and not reflected in ACPI spec.
+ */
+ mp_wake->mailbox_address = 0;
+
apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);
return 0;
--
2.41.0
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