x86/acpi/x86/boot: Add multiprocessor wake-up support

Secondary CPU startup is currently performed with something called
the "INIT/SIPI protocol".  This protocol requires assistance from
VMMs to boot guests.  As should be a familiar story by now, that
support can not be provded to TDX guests because TDX VMMs are
not trusted by guests.

To remedy this situation a new[1] "Multiprocessor Wakeup Structure"
has been added to to an existing ACPI table (MADT).  This structure
provides the physical address of a "mailbox".  A write to the mailbox
then steers the secondary CPU to the boot code.

Add ACPI MADT wake structure parsing support and wake support.  Use
this support to wake CPUs whenever it is present instead of INIT/SIPI.

While this structure can theoretically be used on 32-bit kernels,
there are no 32-bit TDX guest kernels.  It has not been tested and
can not practically *be* tested on 32-bit.  Make it 64-bit only.

1. Details about the new structure can be found in ACPI v6.4, in the
   "Multiprocessor Wakeup Structure" section.

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>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20220405232939.73860-22-kirill.shutemov@linux.intel.com

1 files changed, 10 insertions, 0 deletions

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