arm64: alternative: Allow alternative status checking per cpufeature

In preparation for the application of alternatives at different points
during the boot process, provide the possibility to check whether
alternatives for a feature of interest was already applied instead of
having a global boolean for all alternatives.

Make VHE enablement code check for the VHE feature instead of considering
all alternatives.
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Marc Zyngier <Marc.Zyngier@arm.com>
Cc: Christoffer Dall <Christoffer.Dall@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/alternative.h

@@ -14,8 +14,6 @@
 #include <linux/stddef.h>
 #include <linux/stringify.h>
 
-extern int alternatives_applied;
-
 struct alt_instr {
 	s32 orig_offset;	/* offset to original instruction */
 	s32 alt_offset;		/* offset to replacement instruction */
@@ -28,6 +26,7 @@ typedef void (*alternative_cb_t)(struct alt_instr *alt,
 				 __le32 *origptr, __le32 *updptr, int nr_inst);
 
 void __init apply_alternatives_all(void);
+bool alternative_is_applied(u16 cpufeature);
 
 #ifdef CONFIG_MODULES
 void apply_alternatives_module(void *start, size_t length);

arch/arm64/kernel/alternative.c

@@ -32,13 +32,23 @@
 #define ALT_ORIG_PTR(a)		__ALT_PTR(a, orig_offset)
 #define ALT_REPL_PTR(a)		__ALT_PTR(a, alt_offset)
 
-int alternatives_applied;
+static int all_alternatives_applied;
+
+static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS);
 
 struct alt_region {
 	struct alt_instr *begin;
 	struct alt_instr *end;
 };
 
+bool alternative_is_applied(u16 cpufeature)
+{
+	if (WARN_ON(cpufeature >= ARM64_NCAPS))
+		return false;
+
+	return test_bit(cpufeature, applied_alternatives);
+}
+
 /*
  * Check if the target PC is within an alternative block.
  */
@@ -192,6 +202,9 @@ static void __apply_alternatives(void *alt_region, bool is_module)
 		dsb(ish);
 		__flush_icache_all();
 		isb();
+
+		/* We applied all that was available */
+		bitmap_copy(applied_alternatives, cpu_hwcaps, ARM64_NCAPS);
 	}
 }
 
@@ -208,14 +221,14 @@ static int __apply_alternatives_multi_stop(void *unused)
 
 	/* We always have a CPU 0 at this point (__init) */
 	if (smp_processor_id()) {
-		while (!READ_ONCE(alternatives_applied))
+		while (!READ_ONCE(all_alternatives_applied))
 			cpu_relax();
 		isb();
 	} else {
-		BUG_ON(alternatives_applied);
+		BUG_ON(all_alternatives_applied);
 		__apply_alternatives(&region, false);
 		/* Barriers provided by the cache flushing */
-		WRITE_ONCE(alternatives_applied, 1);
+		WRITE_ONCE(all_alternatives_applied, 1);
 	}
 
 	return 0;

arch/arm64/kernel/cpufeature.c

@@ -1118,7 +1118,7 @@ static void cpu_copy_el2regs(const struct arm64_cpu_capabilities *__unused)
 	 * that, freshly-onlined CPUs will set tpidr_el2, so we don't need to
 	 * do anything here.
 	 */
-	if (!alternatives_applied)
+	if (!alternative_is_applied(ARM64_HAS_VIRT_HOST_EXTN))
 		write_sysreg(read_sysreg(tpidr_el1), tpidr_el2);
 }
 #endif