[tip: x86/cc] x86/acpi: Do not attempt to bring up secondary CPUs in the kexec case

[tip-bot2 for Kirill A. Shutemov]

The following commit has been merged into the x86/cc branch of tip:

Commit-ID:     db0936830a2fcc35e2b283275acf61b6d3ae1e11
Gitweb:        https://git.kernel.org/tip/db0936830a2fcc35e2b283275acf61b6d3ae1e11
Author:        Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
AuthorDate:    Fri, 14 Jun 2024 12:59:00 +03:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Mon, 17 Jun 2024 17:46:17 +02:00

x86/acpi: Do not attempt to bring up secondary CPUs in the kexec case

ACPI MADT doesn't allow to offline a CPU after it was onlined. This limits
kexec: the second kernel won't be able to use more than one CPU.

To prevent a kexec kernel from onlining secondary CPUs, invalidate the mailbox
address in the ACPI MADT wakeup structure which prevents a kexec kernel to use
it.

This is safe as the booting kernel has the mailbox address cached already and
acpi_wakeup_cpu() uses the cached value to bring up the secondary CPUs.

Note: This is a Linux specific convention and not covered by the ACPI
specification.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Tested-by: Tao Liu <ltao@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240614095904.1345461-16-kirill.shutemov@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/acpi/madt_wakeup.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
index 004801b..30820f9 100644
--- a/arch/x86/kernel/acpi/madt_wakeup.c
+++ b/arch/x86/kernel/acpi/madt_wakeup.c
@@ -14,6 +14,11 @@ 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().
 	 *
@@ -64,6 +69,28 @@ static int acpi_wakeup_cpu(u32 apicid, unsigned long start_ip)
 	return 0;
 }
 
+static void acpi_mp_disable_offlining(struct acpi_madt_multiproc_wakeup *mp_wake)
+{
+	cpu_hotplug_disable_offlining();
+
+	/*
+	 * ACPI MADT doesn't allow to offline a CPU after it was onlined. This
+	 * limits kexec: the second kernel won't be able to use more than one CPU.
+	 *
+	 * To prevent a kexec kernel from onlining secondary CPUs invalidate the
+	 * mailbox address in the ACPI MADT wakeup structure which prevents a
+	 * kexec kernel to use it.
+	 *
+	 * This is safe as the booting kernel has the mailbox address cached
+	 * already and acpi_wakeup_cpu() uses the cached value to bring up the
+	 * secondary CPUs.
+	 *
+	 * Note: This is a Linux specific convention and not covered by the
+	 *       ACPI specification.
+	 */
+	mp_wake->mailbox_address = 0;
+}
+
 int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 			      const unsigned long end)
 {
@@ -77,7 +104,7 @@ int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
 
 	acpi_mp_wake_mailbox_paddr = mp_wake->mailbox_address;
 
-	cpu_hotplug_disable_offlining();
+	acpi_mp_disable_offlining(mp_wake);
 
 	apic_update_callback(wakeup_secondary_cpu_64, acpi_wakeup_cpu);