[patch 36/37] x86/smpboot/64: Implement arch_cpuhp_init_parallel_bringup() and enable it

Thomas Gleixner
2023-04-14T23:52:00Z

Implement the validation function which tells the core code whether
parallel bringup is possible:

1) Valid CPUID leaf for APIC ID retrieval. For non x2APIC systmms leaf
0x1 is sufficient, otherwise leaf 0xb or 0x1f must be available.

2) Prevent parallel bringup on encrypted guests as this requires a
different handling of the CPUID leaf retrieval via a call into the
trusted firmware module. This is what the #VC trap handler does later
on, which is not available during the very early startup.

Originally-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/Kconfig | 3 +-
arch/x86/kernel/cpu/common.c | 6 -----
arch/x86/kernel/smpboot.c | 49 +++++++++++++++++++++++++++++++++++++++++--
3 files changed, 50 insertions(+), 8 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -272,8 +272,9 @@ config X86
select HAVE_UNSTABLE_SCHED_CLOCK
select HAVE_USER_RETURN_NOTIFIER
select HAVE_GENERIC_VDSO
+ select HOTPLUG_PARALLEL if SMP && X86_64
select HOTPLUG_SMT if SMP
- select HOTPLUG_SPLIT_STARTUP if SMP
+ select HOTPLUG_SPLIT_STARTUP if SMP && X86_32
select IRQ_FORCED_THREADING
select NEED_PER_CPU_EMBED_FIRST_CHUNK
select NEED_PER_CPU_PAGE_FIRST_CHUNK
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2127,11 +2127,7 @@ static inline void setup_getcpu(int cpu)
}

#ifdef CONFIG_X86_64
-static inline void ucode_cpu_init(int cpu)
-{
- if (cpu)
- load_ucode_ap();
-}
+static inline void ucode_cpu_init(int cpu) { }

static inline void tss_setup_ist(struct tss_struct *tss)
{
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -58,6 +58,7 @@
#include <linux/overflow.h>
#include <linux/stackprotector.h>
#include <linux/cpuhotplug.h>
+#include <linux/mc146818rtc.h>

#include <asm/acpi.h>
#include <asm/cacheinfo.h>
@@ -75,7 +76,7 @@
#include <asm/fpu/api.h>
#include <asm/setup.h>
#include <asm/uv/uv.h>
-#include <linux/mc146818rtc.h>
+#include <asm/microcode.h>
#include <asm/i8259.h>
#include <asm/misc.h>
#include <asm/qspinlock.h>
@@ -128,7 +129,6 @@ int arch_update_cpu_topology(void)
return retval;
}

-
static unsigned int smpboot_warm_reset_vector_count;

static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
@@ -247,6 +247,8 @@ static void notrace start_secondary(void
#endif
cpu_init_exception_handling();

+ load_ucode_ap();
+
/*
* Sync point with the hotplug core. Sets the sync state to ALIVE
* and waits for the control CPU to release it.
@@ -1251,6 +1253,49 @@ void __init smp_prepare_cpus_common(void
set_cpu_sibling_map(0);
}

+#ifdef CONFIG_X86_64
+/* Establish whether parallel bringup can be supported. */
+bool __init arch_cpuhp_init_parallel_bringup(void)
+{
+ unsigned int ctrl;
+
+ if (boot_cpu_data.cpuid_level < 0x01) {
+ pr_info("Parallel CPU startup disabled due to lack of CPUID\n");
+ return false;
+ }
+
+ /* Encrypted guests require special CPUID handling. */
+ if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
+ pr_info("Parallel CPU startup disabled due to guest state encryption\n");
+ return false;
+ }
+
+ switch (topology_extended_leaf) {
+ case 0x0b:
+ ctrl = STARTUP_APICID_CPUID_0B;
+ break;
+ case 0x1f:
+ ctrl = STARTUP_APICID_CPUID_1F;
+ break;
+ case 0x00:
+ /* For !x2APIC mode 8 bits from leaf 0x01 are sufficient. */
+ if (!x2apic_mode) {
+ ctrl = STARTUP_APICID_CPUID_01;
+ break;
+ }
+ fallthrough;
+ default:
+ pr_info("Parallel CPU startup disabled. Unsupported topology leaf %u\n",
+ topology_extended_leaf);
+ return false;
+ }
+
+ pr_debug("Parallel CPU startup enabled: 0x%08x\n", ctrl);
+ smpboot_control = ctrl;
+ return true;
+}
+#endif
+
/*
* Prepare for SMP bootup.
* @max_cpus: configured maximum number of CPUs, It is a legacy parameter