[PATCH v3 1/4] arm64/cpufeature: Store elf_hwcaps as an array rather than unsigned long

[Mark Brown]

When we added support for AT_HWCAP2 we took advantage of the fact that we
have limited hwcaps to the low 32 bits and stored it along with AT_HWCAP
in a single unsigned integer. Thanks to the ever expanding capabilities of
the architecture we have now allocated all 64 of the bits in an unsigned
long so in preparation for adding more hwcaps convert elf_hwcap to be an
array instead. There should be no functional change from this patch.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 arch/arm64/include/asm/cpufeature.h |  6 ++++++
 arch/arm64/include/asm/hwcap.h      |  4 +++-
 arch/arm64/kernel/cpufeature.c      | 22 +++++++++++++++-------
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 14a8f3d93add..6c0284ca703e 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -11,6 +11,12 @@
 #include <asm/hwcap.h>
 #include <asm/sysreg.h>
 
+/*
+ * To support potential future 32 bit only ABIs and/or libc usage we
+ * currently only allocate the bottom 32 bits. Bits 62 and 63 of
+ * AT_HWCAP are reserved for glibc.
+ */
+#define CPU_FEATURES_PER_HWCAP	32
 #define MAX_CPU_FEATURES	64
 #define cpu_feature(x)		KERNEL_HWCAP_ ## x
 
diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
index aa443d8f8cfb..e0054c7b3a98 100644
--- a/arch/arm64/include/asm/hwcap.h
+++ b/arch/arm64/include/asm/hwcap.h
@@ -41,6 +41,8 @@
 #ifndef __ASSEMBLY__
 #include <linux/log2.h>
 
+#define KHWCAP_OFFSET(n)		((n - 1) * CPU_FEATURES_PER_HWCAP)
+
 /*
  * For userspace we represent hwcaps as a collection of HWCAP{,2}_x bitfields
  * as described in uapi/asm/hwcap.h. For the kernel we represent hwcaps as
@@ -85,7 +87,7 @@
 #define KERNEL_HWCAP_PACA		__khwcap_feature(PACA)
 #define KERNEL_HWCAP_PACG		__khwcap_feature(PACG)
 
-#define __khwcap2_feature(x)		(const_ilog2(HWCAP2_ ## x) + 32)
+#define __khwcap2_feature(x)		(const_ilog2(HWCAP2_ ## x) + KHWCAP_OFFSET(2))
 #define KERNEL_HWCAP_DCPODP		__khwcap2_feature(DCPODP)
 #define KERNEL_HWCAP_SVE2		__khwcap2_feature(SVE2)
 #define KERNEL_HWCAP_SVEAES		__khwcap2_feature(SVEAES)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 8d88433de81d..1a8f60a6661e 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -91,7 +91,7 @@
 #include <asm/virt.h>
 
 /* Kernel representation of AT_HWCAP and AT_HWCAP2 */
-static unsigned long elf_hwcap __read_mostly;
+static unsigned long elf_hwcap[MAX_CPU_FEATURES / CPU_FEATURES_PER_HWCAP] __read_mostly;
 
 #ifdef CONFIG_COMPAT
 #define COMPAT_ELF_HWCAP_DEFAULT	\
@@ -3098,14 +3098,22 @@ static bool __maybe_unused __system_matches_cap(unsigned int n)
 
 void cpu_set_feature(unsigned int num)
 {
-	WARN_ON(num >= MAX_CPU_FEATURES);
-	elf_hwcap |= BIT(num);
+	int i = num / CPU_FEATURES_PER_HWCAP;
+	int bit = num % CPU_FEATURES_PER_HWCAP;
+
+	WARN_ON(i >= ARRAY_SIZE(elf_hwcap));
+
+	elf_hwcap[i] |= BIT(bit);
 }
 
 bool cpu_have_feature(unsigned int num)
 {
-	WARN_ON(num >= MAX_CPU_FEATURES);
-	return elf_hwcap & BIT(num);
+	int i = num / CPU_FEATURES_PER_HWCAP;
+	int bit = num % CPU_FEATURES_PER_HWCAP;
+
+	WARN_ON(i >= ARRAY_SIZE(elf_hwcap));
+
+	return elf_hwcap[i] & BIT(bit);
 }
 EXPORT_SYMBOL_GPL(cpu_have_feature);
 
@@ -3116,12 +3124,12 @@ unsigned long cpu_get_elf_hwcap(void)
 	 * note that for userspace compatibility we guarantee that bits 62
 	 * and 63 will always be returned as 0.
 	 */
-	return lower_32_bits(elf_hwcap);
+	return elf_hwcap[0];
 }
 
 unsigned long cpu_get_elf_hwcap2(void)
 {
-	return upper_32_bits(elf_hwcap);
+	return elf_hwcap[1];
 }
 
 static void __init setup_system_capabilities(void)
-- 
2.30.2