arm64: Align boot cpucap handling with system cpucap handling

Currently the detection+enablement of boot cpucaps is separate from the
patching of boot cpucap alternatives, which means there's a period where
cpus_have_cap($CAP) and alternative_has_cap($CAP) may be mismatched.

It would be preferable to manage the boot cpucaps in the same way as the
system cpucaps, both for clarity and to minimize the risk of accidental
usage of code relying upon an alternative which has not yet been
patched.

This patch aligns the handling of boot cpucaps with the handling of
system cpucaps:

* The existing setup_boot_cpu_capabilities() function is moved to be
  closer to the setup_system_capabilities() and setup_system_features()
  functions so that they're more clearly related and more likely to be
  updated together in future.

* The patching of boot cpucap alternatives is moved into
  setup_boot_cpu_capabilities(), immediately after boot cpucaps are
  detected and enabled.

* A new setup_boot_cpu_features() function is added to mirror
  setup_system_features(); this handles initialization of cpucap data
  structures and calls setup_boot_cpu_capabilities(). This makes
  init_cpu_features() a closer mirror to update_cpu_features(), and
  makes smp_prepare_boot_cpu() a closer mirror to smp_cpus_done().

Importantly, while these changes alter the structure of the code, they
retain the existing order of calls to:

  init_cpu_features(); // prefix initializing feature regs
  init_cpucap_indirect_list();
  detect_system_supports_pseudo_nmi();
  update_cpu_capabilities(SCOPE_BOOT_CPU | SCOPE_LOCAL_CPU);
  enable_cpu_capabilities(SCOPE_BOOT_CPU);
  apply_boot_alternatives();

... and hence there should be no functional change as a result of this
patch; this is purely a structural cleanup.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20231212170910.3745497-3-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

3 files changed, 33 insertions, 34 deletions

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index f6d416fe49b0..2ea24c5cb900 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -617,6 +617,7 @@ static inline bool id_aa64pfr1_mte(u64 pfr1)
 	return val >= ID_AA64PFR1_EL1_MTE_MTE2;
 }
 
+void __init setup_boot_cpu_features(void);
 void __init setup_system_features(void);
 void __init setup_user_features(void);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 5f1320c38aa2..e976538c11ac 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1081,25 +1081,6 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
 
 	if (id_aa64pfr1_mte(info->reg_id_aa64pfr1))
 		init_cpu_ftr_reg(SYS_GMID_EL1, info->reg_gmid);
-
-	/*
-	 * Initialize the indirect array of CPU capabilities pointers before we
-	 * handle the boot CPU below.
-	 */
-	init_cpucap_indirect_list();
-
-	/*
-	 * Detect broken pseudo-NMI. Must be called _before_ the call to
-	 * setup_boot_cpu_capabilities() since it interacts with
-	 * can_use_gic_priorities().
-	 */
-	detect_system_supports_pseudo_nmi();
-
-	/*
-	 * Detect and enable early CPU capabilities based on the boot CPU,
-	 * after we have initialised the CPU feature infrastructure.
-	 */
-	setup_boot_cpu_capabilities();
 }
 
 static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new)
@@ -3255,14 +3236,6 @@ void check_local_cpu_capabilities(void)
 		verify_local_cpu_capabilities();
 }
 
-static void __init setup_boot_cpu_capabilities(void)
-{
-	/* Detect capabilities with either SCOPE_BOOT_CPU or SCOPE_LOCAL_CPU */
-	update_cpu_capabilities(SCOPE_BOOT_CPU | SCOPE_LOCAL_CPU);
-	/* Enable the SCOPE_BOOT_CPU capabilities alone right away */
-	enable_cpu_capabilities(SCOPE_BOOT_CPU);
-}
-
 bool this_cpu_has_cap(unsigned int n)
 {
 	if (!WARN_ON(preemptible()) && n < ARM64_NCAPS) {
@@ -3318,6 +3291,36 @@ unsigned long cpu_get_elf_hwcap2(void)
 	return elf_hwcap[1];
 }
 
+static void __init setup_boot_cpu_capabilities(void)
+{
+	/*
+	 * The boot CPU's feature register values have been recorded. Detect
+	 * boot cpucaps and local cpucaps for the boot CPU, then enable and
+	 * patch alternatives for the available boot cpucaps.
+	 */
+	update_cpu_capabilities(SCOPE_BOOT_CPU | SCOPE_LOCAL_CPU);
+	enable_cpu_capabilities(SCOPE_BOOT_CPU);
+	apply_boot_alternatives();
+}
+
+void __init setup_boot_cpu_features(void)
+{
+	/*
+	 * Initialize the indirect array of CPU capabilities pointers before we
+	 * handle the boot CPU.
+	 */
+	init_cpucap_indirect_list();
+
+	/*
+	 * Detect broken pseudo-NMI. Must be called _before_ the call to
+	 * setup_boot_cpu_capabilities() since it interacts with
+	 * can_use_gic_priorities().
+	 */
+	detect_system_supports_pseudo_nmi();
+
+	setup_boot_cpu_capabilities();
+}
+
 static void __init setup_system_capabilities(void)
 {
 	/*
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 85384dc9a89d..4ced34f62dab 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -453,14 +453,9 @@ void __init smp_prepare_boot_cpu(void)
 	 * freed shortly, so we must move over to the runtime per-cpu area.
 	 */
 	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
-	cpuinfo_store_boot_cpu();
 
-	/*
-	 * We now know enough about the boot CPU to apply the
-	 * alternatives that cannot wait until interrupt handling
-	 * and/or scheduling is enabled.
-	 */
-	apply_boot_alternatives();
+	cpuinfo_store_boot_cpu();
+	setup_boot_cpu_features();
 
 	/* Conditionally switch to GIC PMR for interrupt masking */
 	if (system_uses_irq_prio_masking())