arm64: Support AT_HWCAP3

We have filled all 64 bits of AT_HWCAP2 so in order to support discovery of
further features provide the framework to use the already defined AT_HWCAP3
for further CPU features.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20241004-arm64-elf-hwcap3-v2-2-799d1daad8b0@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: broonie

Documentation/arch/arm64/elf_hwcaps.rst

@@ -16,9 +16,9 @@ architected discovery mechanism available to userspace code at EL0. The
 kernel exposes the presence of these features to userspace through a set
 of flags called hwcaps, exposed in the auxiliary vector.
 
-Userspace software can test for features by acquiring the AT_HWCAP or
-AT_HWCAP2 entry of the auxiliary vector, and testing whether the relevant
-flags are set, e.g.::
+Userspace software can test for features by acquiring the AT_HWCAP,
+AT_HWCAP2 or AT_HWCAP3 entry of the auxiliary vector, and testing
+whether the relevant flags are set, e.g.::
 
 	bool floating_point_is_present(void)
 	{

arch/arm64/include/asm/cpufeature.h

@@ -12,7 +12,7 @@
 #include <asm/hwcap.h>
 #include <asm/sysreg.h>
 
-#define MAX_CPU_FEATURES	128
+#define MAX_CPU_FEATURES	192
 #define cpu_feature(x)		KERNEL_HWCAP_ ## x
 
 #define ARM64_SW_FEATURE_OVERRIDE_NOKASLR	0
@@ -438,6 +438,7 @@ void cpu_set_feature(unsigned int num);
 bool cpu_have_feature(unsigned int num);
 unsigned long cpu_get_elf_hwcap(void);
 unsigned long cpu_get_elf_hwcap2(void);
+unsigned long cpu_get_elf_hwcap3(void);
 
 #define cpu_set_named_feature(name) cpu_set_feature(cpu_feature(name))
 #define cpu_have_named_feature(name) cpu_have_feature(cpu_feature(name))

arch/arm64/include/asm/hwcap.h

@@ -159,17 +159,21 @@
 #define KERNEL_HWCAP_SME_SF8DP2		__khwcap2_feature(SME_SF8DP2)
 #define KERNEL_HWCAP_POE		__khwcap2_feature(POE)
 
+#define __khwcap3_feature(x)		(const_ilog2(HWCAP3_ ## x) + 128)
+
 /*
  * This yields a mask that user programs can use to figure out what
  * instruction set this cpu supports.
  */
 #define ELF_HWCAP		cpu_get_elf_hwcap()
 #define ELF_HWCAP2		cpu_get_elf_hwcap2()
+#define ELF_HWCAP3		cpu_get_elf_hwcap3()
 
 #ifdef CONFIG_COMPAT
 #define COMPAT_ELF_HWCAP	(compat_elf_hwcap)
 #define COMPAT_ELF_HWCAP2	(compat_elf_hwcap2)
-extern unsigned int compat_elf_hwcap, compat_elf_hwcap2;
+#define COMPAT_ELF_HWCAP3	(compat_elf_hwcap3)
+extern unsigned int compat_elf_hwcap, compat_elf_hwcap2, compat_elf_hwcap3;
 #endif
 
 enum {

arch/arm64/include/uapi/asm/hwcap.h

@@ -124,4 +124,8 @@
 #define HWCAP2_SME_SF8DP2	(1UL << 62)
 #define HWCAP2_POE		(1UL << 63)
 
+/*
+ * HWCAP3 flags - for AT_HWCAP3
+ */
+
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -103,6 +103,7 @@ static DECLARE_BITMAP(elf_hwcap, MAX_CPU_FEATURES) __read_mostly;
 				 COMPAT_HWCAP_LPAE)
 unsigned int compat_elf_hwcap __read_mostly = COMPAT_ELF_HWCAP_DEFAULT;
 unsigned int compat_elf_hwcap2 __read_mostly;
+unsigned int compat_elf_hwcap3 __read_mostly;
 #endif
 
 DECLARE_BITMAP(system_cpucaps, ARM64_NCAPS);
@@ -3499,6 +3500,11 @@ unsigned long cpu_get_elf_hwcap2(void)
 	return elf_hwcap[1];
 }
 
+unsigned long cpu_get_elf_hwcap3(void)
+{
+	return elf_hwcap[2];
+}
+
 static void __init setup_boot_cpu_capabilities(void)
 {
 	/*