[PATCH RFC v2 2/2] arm64: Support AT_HWCAP3

Mark Brown
2024-10-04T20:31:07Z

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>
---
Documentation/arch/arm64/elf_hwcaps.rst | 6 +++---
arch/arm64/include/asm/cpufeature.h | 3 ++-
arch/arm64/include/asm/hwcap.h | 6 +++++-
arch/arm64/include/uapi/asm/hwcap.h | 4 ++++
arch/arm64/kernel/cpufeature.c | 6 ++++++
5 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/Documentation/arch/arm64/elf_hwcaps.rst b/Documentation/arch/arm64/elf_hwcaps.rst
index 694f67fa07d196816b1292e896ebe6a1b599c125..dc1b11d6d1122bba928b054cd1874aad5073e05c 100644
--- a/Documentation/arch/arm64/elf_hwcaps.rst
+++ b/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)
{
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 3d261cc123c1e22ac7bc9cfcde463624c76b2084..38e7d1a44ea38ab0a06a6f22824ae023b128721b 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/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))
diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
index a775adddecf25633e87d58fb9ac9e6293beac1b3..3b5c50df419ee94193a4d9e3a47516eb0739e89a 100644
--- a/arch/arm64/include/asm/hwcap.h
+++ b/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 {
diff --git a/arch/arm64/include/uapi/asm/hwcap.h b/arch/arm64/include/uapi/asm/hwcap.h
index 055381b2c61595361c2d57d38be936c2dfeaa195..3dd4a53a438a14bfb41882b2ab15bdd7ce617475 100644
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/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 */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 718728a85430fad5151b73fa213a510efac3f834..7221636b790709b153b49126e00246cc3032a7bc 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/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)
{
/*

--
2.39.2