arm64: Keep track of CPU feature registers

This patch adds an infrastructure to keep track of the CPU feature
registers on the system. For each register, the infrastructure keeps
track of the system wide safe value of the feature bits. Also, tracks
the which fields of a register should be matched strictly across all
the CPUs on the system for the SANITY check infrastructure.

The feature bits are classified into following 3 types depending on
the implication of the possible values. This information is used to
decide the safe value for a feature.

LOWER_SAFE  - The smaller value is safer
HIGHER_SAFE - The bigger value is safer
EXACT       - We can't decide between the two, so a predefined safe_value is used.

This infrastructure will be later used to make better decisions for:

 - Kernel features (e.g, KVM, Debug)
 - SANITY Check
 - CPU capability
 - ELF HWCAP
 - Exposing CPU Feature register to userspace.

Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
Tested-by: Dave Martin <Dave.Martin@arm.com>
[catalin.marinas@arm.com: whitespace fix]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 85507fecf287..01bb5cf995af 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -35,6 +35,37 @@
 
 #include <linux/kernel.h>
 
+/* CPU feature register tracking */
+enum ftr_type {
+	FTR_EXACT,	/* Use a predefined safe value */
+	FTR_LOWER_SAFE,	/* Smaller value is safe */
+	FTR_HIGHER_SAFE,/* Bigger value is safe */
+};
+
+#define FTR_STRICT	true	/* SANITY check strict matching required */
+#define FTR_NONSTRICT	false	/* SANITY check ignored */
+
+struct arm64_ftr_bits {
+	bool		strict;	  /* CPU Sanity check: strict matching required ? */
+	enum ftr_type	type;
+	u8		shift;
+	u8		width;
+	s64		safe_val; /* safe value for discrete features */
+};
+
+/*
+ * @arm64_ftr_reg - Feature register
+ * @strict_mask		Bits which should match across all CPUs for sanity.
+ * @sys_val		Safe value across the CPUs (system view)
+ */
+struct arm64_ftr_reg {
+	u32			sys_id;
+	const char		*name;
+	u64			strict_mask;
+	u64			sys_val;
+	struct arm64_ftr_bits	*ftr_bits;
+};
+
 struct arm64_cpu_capabilities {
 	const char *desc;
 	u16 capability;
@@ -88,6 +119,16 @@ cpuid_feature_extract_field(u64 features, int field)
 	return cpuid_feature_extract_field_width(features, field, 4);
 }
 
+static inline u64 arm64_ftr_mask(struct arm64_ftr_bits *ftrp)
+{
+	return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);
+}
+
+static inline s64 arm64_ftr_value(struct arm64_ftr_bits *ftrp, u64 val)
+{
+	return cpuid_feature_extract_field_width(val, ftrp->shift, ftrp->width);
+}
+
 static inline bool id_aa64mmfr0_mixed_endian_el0(u64 mmfr0)
 {
 	return cpuid_feature_extract_field(mmfr0, ID_AA64MMFR0_BIGENDEL_SHIFT) == 0x1 ||