[PATCH v3 0/9] arm64: Expose CPUID registers via emulation

[PATCH v3 0/9] arm64: Expose CPUID registers via emulation

[Suzuki K Poulose]

This series adds a new ABI to expose the CPU feature registers
to the user space via emulation of MRS instruction. The system exposes
only a limited set of feature values (See the documentation patch)
from the cpufeature infrastructure. The feature bits that are not
exposed are set to the 'safe value' which implies 'not supported'.

Apart from the selected feature registers, we expose MIDR_EL1 (Main
ID Register). The user should be aware that, reading MIDR_EL1 can be
tricky on a heterogeneous system (just like getcpu()). We export the
value of the current CPU where 'MRS' is executed.

Applies on v4.10-rc2.

Changes since V2:
 - Mark DCZID_EL0 fields visible, as the register is already accessible
   to EL0.
 - Included the sample program to demonstrate the use of the new ABI in
   documentation.
 - Fixed minor coding style issues.

Changes since V1:
  - Drop mask for Op0 in sys_reg()
  - Fix documentation
  - Change safe value of MPIDR to drop MT support
  - Do not emulate AArch32 ID registers

Mark Rutland (2):
  arm64: cpufeature: treat unknown fields as RES0
  arm64: cpufeature: remove explicit RAZ fields

Suzuki K Poulose (7):
  arm64: cpufeature: Cleanup feature bit tables
  arm64: cpufeature: Document the rules of safe value for features
  arm64: cpufeature: Define helpers for sys_reg id
  arm64: Add helper to decode register from instruction
  arm64: cpufeature: Track user visible fields
  arm64: cpufeature: Expose CPUID registers by emulation
  arm64: Documentation - Expose CPU feature registers

 Documentation/arm64/cpu-feature-registers.txt | 265 ++++++++++++++++++++
 arch/arm64/include/asm/cpufeature.h           |  27 +-
 arch/arm64/include/asm/insn.h                 |   2 +
 arch/arm64/include/asm/sysreg.h               |  25 +-
 arch/arm64/include/uapi/asm/hwcap.h           |   1 +
 arch/arm64/kernel/cpufeature.c                | 340 +++++++++++++++++---------
 arch/arm64/kernel/cpuinfo.c                   |   1 +
 arch/arm64/kernel/insn.c                      |  29 +++
 arch/arm64/kernel/traps.c                     |   2 +-
 9 files changed, 571 insertions(+), 121 deletions(-)
 create mode 100644 Documentation/arm64/cpu-feature-registers.txt

-- 
2.7.4

[PATCH v3 1/9] arm64: cpufeature: treat unknown fields as RES0

[Suzuki K Poulose]

From: Mark Rutland <mark.rutland@arm.com>

Any fields not defined in an arm64_ftr_bits entry are propagated to the
system-wide register value in init_cpu_ftr_reg(), and while we require
that these strictly match for the sanity checks, we don't update them in
update_cpu_ftr_reg().

Generally, the lack of an arm64_ftr_bits entry indicates that the bits
are currently RES0 (as is the case for the upper 32 bits of all
supposedly 32-bit registers).

A better default would be to use zero for the system-wide value of
unallocated bits, making all register checking consistent, and allowing
for subsequent simplifications to the arm64_ftr_bits arrays.

This patch updates init_cpu_ftr_reg() to treat unallocated bits as RES0
for the purpose of the system-wide safe value. These bits will still be
sanity checked with strict match requirements, as is currently the case.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/kernel/cpufeature.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index fdf8f04..ea02201 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -410,23 +410,33 @@ static void __init sort_ftr_regs(void)
 /*
  * Initialise the CPU feature register from Boot CPU values.
  * Also initiliases the strict_mask for the register.
+ * Any bits that are not covered by an arm64_ftr_bits entry are considered
+ * RES0 for the system-wide value, and must strictly match.
  */
 static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
 {
 	u64 val = 0;
 	u64 strict_mask = ~0x0ULL;
+	u64 valid_mask = 0;
+
 	const struct arm64_ftr_bits *ftrp;
 	struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg);
 
 	BUG_ON(!reg);
 
 	for (ftrp  = reg->ftr_bits; ftrp->width; ftrp++) {
+		u64 ftr_mask = arm64_ftr_mask(ftrp);
 		s64 ftr_new = arm64_ftr_value(ftrp, new);
 
 		val = arm64_ftr_set_value(ftrp, val, ftr_new);
+
+		valid_mask |= ftr_mask;
 		if (!ftrp->strict)
-			strict_mask &= ~arm64_ftr_mask(ftrp);
+			strict_mask &= ~ftr_mask;
 	}
+
+	val &= valid_mask;
+
 	reg->sys_val = val;
 	reg->strict_mask = strict_mask;
 }
-- 
2.7.4

[PATCH v3 2/9] arm64: cpufeature: remove explicit RAZ fields

[Suzuki K Poulose]

From: Mark Rutland <mark.rutland@arm.com>

We currently have some RAZ fields described explicitly in our
arm64_ftr_bits arrays. These are inconsistently commented, grouped,
and/or applied, and maintaining these is error-prone.

Luckily, we don't need these at all. We'll never need to inspect RAZ
fields to determine feature support, and init_cpu_ftr_reg() will ensure
that any bits without a corresponding arm64_ftr_bits entry are treated
as RES0 with strict matching requirements. In check_update_ftr_reg()
we'll then compare these bits from the relevant cpuinfo_arm64
structures, and need not store them in a arm64_ftr_reg.

This patch removes the unnecessary arm64_ftr_bits entries for RES0 bits.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/kernel/cpufeature.c | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index ea02201..72bda9d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -81,21 +81,16 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 
 
 static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 24, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 4, 0),	/* RAZ */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 28, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0),
 	S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
 	S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_FP_SHIFT, 4, ID_AA64PFR0_FP_NI),
@@ -108,7 +103,6 @@ static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64mmfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
 	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN4_SHIFT, 4, ID_AA64MMFR0_TGRAN4_NI),
 	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN64_SHIFT, 4, ID_AA64MMFR0_TGRAN64_NI),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN16_SHIFT, 4, ID_AA64MMFR0_TGRAN16_NI),
@@ -126,7 +120,6 @@ static const struct arm64_ftr_bits ftr_id_aa64mmfr0[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64mmfr1[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR1_PAN_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_LOR_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_HPD_SHIFT, 4, 0),
@@ -147,7 +140,6 @@ static const struct arm64_ftr_bits ftr_id_aa64mmfr2[] = {
 
 static const struct arm64_ftr_bits ftr_ctr[] = {
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 31, 1, 1),	/* RAO */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 28, 3, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_HIGHER_SAFE, 24, 4, 0),	/* CWG */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),	/* ERG */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 1),	/* DminLine */
@@ -157,7 +149,6 @@ static const struct arm64_ftr_bits ftr_ctr[] = {
 	 * If we have differing I-cache policies, report it as the weakest - AIVIVT.
 	 */
 	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_EXACT, 14, 2, ICACHE_POLICY_AIVIVT),	/* L1Ip */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 10, 0),	/* RAZ */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),	/* IminLine */
 	ARM64_FTR_END,
 };
@@ -191,14 +182,12 @@ static const struct arm64_ftr_bits ftr_id_aa64dfr0[] = {
 };
 
 static const struct arm64_ftr_bits ftr_mvfr2[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 8, 24, 0),	/* RAZ */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* FPMisc */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 4, 0),		/* SIMDMisc */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_dczid[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 5, 27, 0),	/* RAZ */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 1, 1),		/* DZP */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),	/* BS */
 	ARM64_FTR_END,
@@ -207,7 +196,6 @@ static const struct arm64_ftr_bits ftr_dczid[] = {
 
 static const struct arm64_ftr_bits ftr_id_isar5[] = {
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_RDM_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 20, 4, 0),	/* RAZ */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_CRC32_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_SHA2_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_SHA1_SHIFT, 4, 0),
@@ -217,14 +205,11 @@ static const struct arm64_ftr_bits ftr_id_isar5[] = {
 };
 
 static const struct arm64_ftr_bits ftr_id_mmfr4[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 8, 24, 0),	/* RAZ */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* ac2 */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 4, 0),		/* RAZ */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_pfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 16, 16, 0),	/* RAZ */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 12, 4, 0),	/* State3 */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 8, 4, 0),		/* State2 */
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* State1 */
-- 
2.7.4

[PATCH v3 3/9] arm64: cpufeature: Cleanup feature bit tables

[Suzuki K Poulose]

This patch does the following clean ups :

1) All undescribed fields of a register are now treated as "strict"
   with a safe value of 0. Hence we could leave an empty table for
   describing registers which are RAZ.

2) ID_AA64DFR1_EL1 is RAZ and should use the table for RAZ register.

3) ftr_generic32 is used to represent a register with a 32bit feature
   value. Rename this to ftr_singl32 to make it more obvious. Since
   we don't have a 64bit singe feature register, kill ftr_generic.

Based on a patch by Mark Rutland.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/kernel/cpufeature.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 72bda9d..fb519e1 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -247,18 +247,13 @@ static const struct arm64_ftr_bits ftr_generic_32bits[] = {
 	ARM64_FTR_END,
 };
 
-static const struct arm64_ftr_bits ftr_generic[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 64, 0),
-	ARM64_FTR_END,
-};
-
-static const struct arm64_ftr_bits ftr_generic32[] = {
+/* Table for a single 32bit feature value */
+static const struct arm64_ftr_bits ftr_single32[] = {
 	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 32, 0),
 	ARM64_FTR_END,
 };
 
-static const struct arm64_ftr_bits ftr_aa64raz[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 64, 0),
+static const struct arm64_ftr_bits ftr_raz[] = {
 	ARM64_FTR_END,
 };
 
@@ -299,15 +294,15 @@ static const struct __ftr_reg_entry {
 
 	/* Op1 = 0, CRn = 0, CRm = 4 */
 	ARM64_FTR_REG(SYS_ID_AA64PFR0_EL1, ftr_id_aa64pfr0),
-	ARM64_FTR_REG(SYS_ID_AA64PFR1_EL1, ftr_aa64raz),
+	ARM64_FTR_REG(SYS_ID_AA64PFR1_EL1, ftr_raz),
 
 	/* Op1 = 0, CRn = 0, CRm = 5 */
 	ARM64_FTR_REG(SYS_ID_AA64DFR0_EL1, ftr_id_aa64dfr0),
-	ARM64_FTR_REG(SYS_ID_AA64DFR1_EL1, ftr_generic),
+	ARM64_FTR_REG(SYS_ID_AA64DFR1_EL1, ftr_raz),
 
 	/* Op1 = 0, CRn = 0, CRm = 6 */
 	ARM64_FTR_REG(SYS_ID_AA64ISAR0_EL1, ftr_id_aa64isar0),
-	ARM64_FTR_REG(SYS_ID_AA64ISAR1_EL1, ftr_aa64raz),
+	ARM64_FTR_REG(SYS_ID_AA64ISAR1_EL1, ftr_raz),
 
 	/* Op1 = 0, CRn = 0, CRm = 7 */
 	ARM64_FTR_REG(SYS_ID_AA64MMFR0_EL1, ftr_id_aa64mmfr0),
@@ -319,7 +314,7 @@ static const struct __ftr_reg_entry {
 	ARM64_FTR_REG(SYS_DCZID_EL0, ftr_dczid),
 
 	/* Op1 = 3, CRn = 14, CRm = 0 */
-	ARM64_FTR_REG(SYS_CNTFRQ_EL0, ftr_generic32),
+	ARM64_FTR_REG(SYS_CNTFRQ_EL0, ftr_single32),
 };
 
 static int search_cmp_ftr_reg(const void *id, const void *regp)
-- 
2.7.4

[PATCH v3 4/9] arm64: cpufeature: Document the rules of safe value for features

[Suzuki K Poulose]

Document the rules for choosing the safe value for different types
of features.

Cc: Dave Martin <dave.martin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index b4989df..fb76c81 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -29,7 +29,21 @@
 #include <linux/jump_label.h>
 #include <linux/kernel.h>
 
-/* CPU feature register tracking */
+/*
+ * CPU feature register tracking
+ *
+ * The safe value of a CPUID feature field is dependent on the implications
+ * of the values assigned to it by the architecture. Based on the relationship
+ * between the values, the features are classified into 3 types.
+ *
+ * a) LOWER_SAFE - The value 'n+1' indicates, value 'n' and some
+ *    additional features. (where n >= 0). The smaller value (n) is
+ *    considered safer in this case.
+ * b) HIGHER_SAFE - The value 'n+1' is safer than 'n' (for n>= 0).
+ * c) EXACT - If the values of the feature don't have any relationship,
+ *    a predefined safe value is used.
+ */
+
 enum ftr_type {
 	FTR_EXACT,	/* Use a predefined safe value */
 	FTR_LOWER_SAFE,	/* Smaller value is safe */
-- 
2.7.4

[PATCH v3 5/9] arm64: cpufeature: Define helpers for sys_reg id

[Suzuki K Poulose]

Define helper macros to extract op0, op1, CRn, CRm & op2
for a given sys_reg id. While at it remove the explicit
masking only used for Op0.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/sysreg.h | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 98ae03f..cf43064 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -32,8 +32,27 @@
  *	[11-8]  : CRm
  *	[7-5]   : Op2
  */
+#define Op0_shift	19
+#define Op0_mask	0x3
+#define Op1_shift	16
+#define Op1_mask	0x7
+#define CRn_shift	12
+#define CRn_mask	0xf
+#define CRm_shift	8
+#define CRm_mask	0xf
+#define Op2_shift	5
+#define Op2_mask	0x7
+
 #define sys_reg(op0, op1, crn, crm, op2) \
-	((((op0)&3)<<19)|((op1)<<16)|((crn)<<12)|((crm)<<8)|((op2)<<5))
+	(((op0) << Op0_shift) | ((op1) << Op1_shift) | \
+	 ((crn) << CRn_shift) | ((crm) << CRm_shift) | \
+	 ((op2) << Op2_shift))
+
+#define sys_reg_Op0(id)	(((id) >> Op0_shift) & Op0_mask)
+#define sys_reg_Op1(id)	(((id) >> Op1_shift) & Op1_mask)
+#define sys_reg_CRn(id)	(((id) >> CRn_shift) & CRn_mask)
+#define sys_reg_CRm(id)	(((id) >> CRm_shift) & CRm_mask)
+#define sys_reg_Op2(id)	(((id) >> Op2_shift) & Op2_mask)
 
 #ifndef CONFIG_BROKEN_GAS_INST
 
-- 
2.7.4

[PATCH v3 6/9] arm64: Add helper to decode register from instruction

[Suzuki K Poulose]

Add a helper to extract the register field from a given
instruction.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/insn.h |  2 ++
 arch/arm64/kernel/insn.c      | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index bc85366..aecc07e 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -332,6 +332,8 @@ bool aarch64_insn_is_branch(u32 insn);
 u64 aarch64_insn_decode_immediate(enum aarch64_insn_imm_type type, u32 insn);
 u32 aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
 				  u32 insn, u64 imm);
+u32 aarch64_insn_decode_register(enum aarch64_insn_register_type type,
+					 u32 insn);
 u32 aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
 				enum aarch64_insn_branch_type type);
 u32 aarch64_insn_gen_comp_branch_imm(unsigned long pc, unsigned long addr,
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index 94b62c1..1f44cf8 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -417,6 +417,35 @@ u32 __kprobes aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
 	return insn;
 }
 
+u32 aarch64_insn_decode_register(enum aarch64_insn_register_type type,
+					u32 insn)
+{
+	int shift;
+
+	switch (type) {
+	case AARCH64_INSN_REGTYPE_RT:
+	case AARCH64_INSN_REGTYPE_RD:
+		shift = 0;
+		break;
+	case AARCH64_INSN_REGTYPE_RN:
+		shift = 5;
+		break;
+	case AARCH64_INSN_REGTYPE_RT2:
+	case AARCH64_INSN_REGTYPE_RA:
+		shift = 10;
+		break;
+	case AARCH64_INSN_REGTYPE_RM:
+		shift = 16;
+		break;
+	default:
+		pr_err("%s: unknown register type encoding %d\n", __func__,
+		       type);
+		return 0;
+	}
+
+	return (insn >> shift) & GENMASK(4, 0);
+}
+
 static u32 aarch64_insn_encode_register(enum aarch64_insn_register_type type,
 					u32 insn,
 					enum aarch64_insn_register reg)
-- 
2.7.4

[PATCH v3 7/9] arm64: cpufeature: Track user visible fields

[Suzuki K Poulose]

Track the user visible fields of a CPU feature register. This will be
used for exposing the value to the userspace. All the user visible
fields of a feature register will be passed on as it is, while the
others would be filled with their respective safe value.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
Changes since V2:
 - Mark DCZID_EL0 fields visible, as the register is already accessible
   to EL0.
---
 arch/arm64/include/asm/cpufeature.h |  11 +++
 arch/arm64/kernel/cpufeature.c      | 189 +++++++++++++++++++-----------------
 arch/arm64/kernel/traps.c           |   2 +-
 3 files changed, 111 insertions(+), 91 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index fb76c81..c5ebc44 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -56,8 +56,12 @@ enum ftr_type {
 #define FTR_SIGNED	true	/* Value should be treated as signed */
 #define FTR_UNSIGNED	false	/* Value should be treated as unsigned */
 
+#define FTR_VISIBLE	true	/* Feature visible to the user space */
+#define FTR_HIDDEN	false	/* Feature is hidden from the user */
+
 struct arm64_ftr_bits {
 	bool		sign;	/* Value is signed ? */
+	bool		visible;
 	bool		strict;	/* CPU Sanity check: strict matching required ? */
 	enum ftr_type	type;
 	u8		shift;
@@ -73,7 +77,9 @@ struct arm64_ftr_bits {
 struct arm64_ftr_reg {
 	const char			*name;
 	u64				strict_mask;
+	u64				user_mask;
 	u64				sys_val;
+	u64				user_val;
 	const struct arm64_ftr_bits	*ftr_bits;
 };
 
@@ -173,6 +179,11 @@ static inline u64 arm64_ftr_mask(const struct arm64_ftr_bits *ftrp)
 	return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);
 }
 
+static inline u64 arm64_ftr_reg_user_value(const struct arm64_ftr_reg *reg)
+{
+	return (reg->user_val | (reg->sys_val & reg->user_mask));
+}
+
 static inline int __attribute_const__
 cpuid_feature_extract_field(u64 features, int field, bool sign)
 {
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index fb519e1..474c450 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -52,9 +52,10 @@ EXPORT_SYMBOL(cpu_hwcaps);
 DEFINE_STATIC_KEY_ARRAY_FALSE(cpu_hwcap_keys, ARM64_NCAPS);
 EXPORT_SYMBOL(cpu_hwcap_keys);
 
-#define __ARM64_FTR_BITS(SIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
+#define __ARM64_FTR_BITS(SIGNED, VISIBLE, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
 	{						\
 		.sign = SIGNED,				\
+		.visible = VISIBLE,			\
 		.strict = STRICT,			\
 		.type = TYPE,				\
 		.shift = SHIFT,				\
@@ -63,12 +64,12 @@ EXPORT_SYMBOL(cpu_hwcap_keys);
 	}
 
 /* Define a feature with unsigned values */
-#define ARM64_FTR_BITS(STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
-	__ARM64_FTR_BITS(FTR_UNSIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL)
+#define ARM64_FTR_BITS(VISIBLE, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
+	__ARM64_FTR_BITS(FTR_UNSIGNED, VISIBLE, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL)
 
 /* Define a feature with a signed value */
-#define S_ARM64_FTR_BITS(STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
-	__ARM64_FTR_BITS(FTR_SIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL)
+#define S_ARM64_FTR_BITS(VISIBLE, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
+	__ARM64_FTR_BITS(FTR_SIGNED, VISIBLE, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL)
 
 #define ARM64_FTR_END					\
 	{						\
@@ -81,75 +82,75 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 
 
 static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0),
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_FP_SHIFT, 4, ID_AA64PFR0_FP_NI),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0),
+	S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
+	S_ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_FP_SHIFT, 4, ID_AA64PFR0_FP_NI),
 	/* Linux doesn't care about the EL3 */
-	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_EXACT, ID_AA64PFR0_EL3_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL2_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL1_SHIFT, 4, ID_AA64PFR0_EL1_64BIT_ONLY),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL0_SHIFT, 4, ID_AA64PFR0_EL0_64BIT_ONLY),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_EXACT, ID_AA64PFR0_EL3_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL2_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL1_SHIFT, 4, ID_AA64PFR0_EL1_64BIT_ONLY),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64PFR0_EL0_SHIFT, 4, ID_AA64PFR0_EL0_64BIT_ONLY),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64mmfr0[] = {
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN4_SHIFT, 4, ID_AA64MMFR0_TGRAN4_NI),
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN64_SHIFT, 4, ID_AA64MMFR0_TGRAN64_NI),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN16_SHIFT, 4, ID_AA64MMFR0_TGRAN16_NI),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_BIGENDEL0_SHIFT, 4, 0),
+	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN4_SHIFT, 4, ID_AA64MMFR0_TGRAN4_NI),
+	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN64_SHIFT, 4, ID_AA64MMFR0_TGRAN64_NI),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_TGRAN16_SHIFT, 4, ID_AA64MMFR0_TGRAN16_NI),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_BIGENDEL0_SHIFT, 4, 0),
 	/* Linux shouldn't care about secure memory */
-	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_EXACT, ID_AA64MMFR0_SNSMEM_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_BIGENDEL_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_ASID_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_EXACT, ID_AA64MMFR0_SNSMEM_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_BIGENDEL_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR0_ASID_SHIFT, 4, 0),
 	/*
 	 * Differing PARange is fine as long as all peripherals and memory are mapped
 	 * within the minimum PARange of all CPUs
 	 */
-	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64MMFR0_PARANGE_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64MMFR0_PARANGE_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64mmfr1[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR1_PAN_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_LOR_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_HPD_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_VHE_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_VMIDBITS_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_HADBS_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR1_PAN_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_LOR_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_HPD_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_VHE_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_VMIDBITS_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR1_HADBS_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64mmfr2[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_LVA_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_IESB_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_LSM_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_UAO_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_CNP_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_LVA_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_IESB_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_LSM_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_UAO_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64MMFR2_CNP_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_ctr[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 31, 1, 1),	/* RAO */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_HIGHER_SAFE, 24, 4, 0),	/* CWG */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),	/* ERG */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 1),	/* DminLine */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, 31, 1, 1),	/* RAO */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_HIGHER_SAFE, 24, 4, 0),	/* CWG */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),	/* ERG */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 1),	/* DminLine */
 	/*
 	 * Linux can handle differing I-cache policies. Userspace JITs will
 	 * make use of *minLine.
 	 * If we have differing I-cache policies, report it as the weakest - AIVIVT.
 	 */
-	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_EXACT, 14, 2, ICACHE_POLICY_AIVIVT),	/* L1Ip */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),	/* IminLine */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_EXACT, 14, 2, ICACHE_POLICY_AIVIVT),	/* L1Ip */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),	/* IminLine */
 	ARM64_FTR_END,
 };
 
@@ -159,73 +160,73 @@ struct arm64_ftr_reg arm64_ftr_reg_ctrel0 = {
 };
 
 static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 28, 4, 0xf),	/* InnerShr */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 24, 4, 0),	/* FCSE */
-	ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, 20, 4, 0),	/* AuxReg */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 16, 4, 0),	/* TCM */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 12, 4, 0),	/* ShareLvl */
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 8, 4, 0xf),	/* OuterShr */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),	/* PMSA */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 4, 0),	/* VMSA */
+	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 28, 4, 0xf),	/* InnerShr */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 24, 4, 0),	/* FCSE */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_LOWER_SAFE, 20, 4, 0),	/* AuxReg */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 16, 4, 0),	/* TCM */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 12, 4, 0),	/* ShareLvl */
+	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 8, 4, 0xf),	/* OuterShr */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 4, 4, 0),	/* PMSA */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 0, 4, 0),	/* VMSA */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_aa64dfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_CTX_CMPS_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_WRPS_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_BRPS_SHIFT, 4, 0),
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64DFR0_PMUVER_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64DFR0_TRACEVER_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64DFR0_DEBUGVER_SHIFT, 4, 0x6),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 32, 32, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_CTX_CMPS_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_WRPS_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_BRPS_SHIFT, 4, 0),
+	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64DFR0_PMUVER_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64DFR0_TRACEVER_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64DFR0_DEBUGVER_SHIFT, 4, 0x6),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_mvfr2[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* FPMisc */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 4, 0),		/* SIMDMisc */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* FPMisc */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 0, 4, 0),		/* SIMDMisc */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_dczid[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 1, 1),		/* DZP */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),	/* BS */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_EXACT, 4, 1, 1),		/* DZP */
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),	/* BS */
 	ARM64_FTR_END,
 };
 
 
 static const struct arm64_ftr_bits ftr_id_isar5[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_RDM_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_CRC32_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_SHA2_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_SHA1_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_AES_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_ISAR5_SEVL_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_ISAR5_RDM_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_ISAR5_CRC32_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_ISAR5_SHA2_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_ISAR5_SHA1_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_ISAR5_AES_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_ISAR5_SEVL_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_mmfr4[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* ac2 */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* ac2 */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_pfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 12, 4, 0),	/* State3 */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 8, 4, 0),		/* State2 */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* State1 */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 4, 0),		/* State0 */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 12, 4, 0),	/* State3 */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 8, 4, 0),		/* State2 */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 4, 4, 0),		/* State1 */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 0, 4, 0),		/* State0 */
 	ARM64_FTR_END,
 };
 
 static const struct arm64_ftr_bits ftr_id_dfr0[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 28, 4, 0),
-	S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 24, 4, 0xf),	/* PerfMon */
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 12, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 8, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 4, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 28, 4, 0),
+	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 24, 4, 0xf),	/* PerfMon */
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 12, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 8, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 4, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),
 	ARM64_FTR_END,
 };
 
@@ -236,20 +237,20 @@ static const struct arm64_ftr_bits ftr_id_dfr0[] = {
  * id_isar[0-4], id_mmfr[1-3], id_pfr1, mvfr[0-1]
  */
 static const struct arm64_ftr_bits ftr_generic_32bits[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 28, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 24, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 12, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 8, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 4, 4, 0),
-	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 28, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 24, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 20, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 16, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 12, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 8, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 4, 4, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, 0, 4, 0),
 	ARM64_FTR_END,
 };
 
 /* Table for a single 32bit feature value */
 static const struct arm64_ftr_bits ftr_single32[] = {
-	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 0, 32, 0),
+	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, 0, 32, 0),
 	ARM64_FTR_END,
 };
 
@@ -397,6 +398,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
 {
 	u64 val = 0;
 	u64 strict_mask = ~0x0ULL;
+	u64 user_mask = 0;
 	u64 valid_mask = 0;
 
 	const struct arm64_ftr_bits *ftrp;
@@ -413,12 +415,19 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
 		valid_mask |= ftr_mask;
 		if (!ftrp->strict)
 			strict_mask &= ~ftr_mask;
+		if (ftrp->visible)
+			user_mask |= ftr_mask;
+		else
+			reg->user_val = arm64_ftr_set_value(ftrp,
+							    reg->user_val,
+							    ftrp->safe_val);
 	}
 
 	val &= valid_mask;
 
 	reg->sys_val = val;
 	reg->strict_mask = strict_mask;
+	reg->user_mask = user_mask;
 }
 
 void __init init_cpu_features(struct cpuinfo_arm64 *info)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 5b830be..8187229 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -496,7 +496,7 @@ static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
 {
 	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
 
-	regs->regs[rt] = arm64_ftr_reg_ctrel0.sys_val;
+	regs->regs[rt] = arm64_ftr_reg_user_value(&arm64_ftr_reg_ctrel0);
 	regs->pc += 4;
 }
 
-- 
2.7.4

[PATCH v3 8/9] arm64: cpufeature: Expose CPUID registers by emulation

[Suzuki K Poulose]

This patch adds the hook for emulating MRS instruction to
export the 'user visible' value of supported system registers.
We emulate only the following id space for system registers:

 Op0=3, Op1=0, CRn=0, CRm=[0, 4-7]

The rest will fall back to SIGILL. This capability is also
advertised via a new HWCAP_CPUID.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 arch/arm64/include/asm/sysreg.h     |   4 ++
 arch/arm64/include/uapi/asm/hwcap.h |   1 +
 arch/arm64/kernel/cpufeature.c      | 101 ++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/cpuinfo.c         |   1 +
 4 files changed, 107 insertions(+)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index cf43064..86a207a 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -264,6 +264,10 @@
 #define ID_AA64MMFR0_TGRAN_SUPPORTED	ID_AA64MMFR0_TGRAN64_SUPPORTED
 #endif
 
+
+/* Safe value for MPIDR_EL1: Bit31:RES1, Bit30:U:0, Bit24:MT:0 */
+#define SYS_MPIDR_SAFE_VAL		(1UL << 31)
+
 #ifdef __ASSEMBLY__
 
 	.irp	num,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30
diff --git a/arch/arm64/include/uapi/asm/hwcap.h b/arch/arm64/include/uapi/asm/hwcap.h
index a739287..773c90b 100644
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/arch/arm64/include/uapi/asm/hwcap.h
@@ -30,5 +30,6 @@
 #define HWCAP_ATOMICS		(1 << 8)
 #define HWCAP_FPHP		(1 << 9)
 #define HWCAP_ASIMDHP		(1 << 10)
+#define HWCAP_CPUID		(1 << 11)
 
 #endif /* _UAPI__ASM_HWCAP_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 474c450..bb635a7 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -29,6 +29,7 @@
 #include <asm/mmu_context.h>
 #include <asm/processor.h>
 #include <asm/sysreg.h>
+#include <asm/traps.h>
 #include <asm/virt.h>
 
 unsigned long elf_hwcap __read_mostly;
@@ -932,6 +933,8 @@ static bool cpus_have_elf_hwcap(const struct arm64_cpu_capabilities *cap)
 
 static void __init setup_elf_hwcaps(const struct arm64_cpu_capabilities *hwcaps)
 {
+	/* We support emulation of accesses to CPU ID feature registers */
+	elf_hwcap |= HWCAP_CPUID;
 	for (; hwcaps->matches; hwcaps++)
 		if (hwcaps->matches(hwcaps, hwcaps->def_scope))
 			cap_set_elf_hwcap(hwcaps);
@@ -1119,3 +1122,101 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
 {
 	return (cpus_have_const_cap(ARM64_HAS_PAN) && !cpus_have_const_cap(ARM64_HAS_UAO));
 }
+
+/*
+ * We emulate only the following system register space.
+ * Op0 = 0x3, CRn = 0x0, Op1 = 0x0, CRm = [0, 4 - 7]
+ * See Table C5-6 System instruction encodings for System register accesses,
+ * ARMv8 ARM(ARM DDI 0487A.f) for more details.
+ */
+static inline bool __attribute_const__ is_emulated(u32 id)
+{
+	return (sys_reg_Op0(id) == 0x3 &&
+		sys_reg_CRn(id) == 0x0 &&
+		sys_reg_Op1(id) == 0x0 &&
+		(sys_reg_CRm(id) == 0 ||
+		 ((sys_reg_CRm(id) >= 4) && (sys_reg_CRm(id) <= 7))));
+}
+
+/*
+ * With CRm == 0, reg should be one of :
+ * MIDR_EL1, MPIDR_EL1 or REVIDR_EL1.
+ */
+static inline int emulate_id_reg(u32 id, u64 *valp)
+{
+	switch (id) {
+	case SYS_MIDR_EL1:
+		*valp = read_cpuid_id();
+		break;
+	case SYS_MPIDR_EL1:
+		*valp = SYS_MPIDR_SAFE_VAL;
+		break;
+	case SYS_REVIDR_EL1:
+		/* IMPLEMENTATION DEFINED values are emulated with 0 */
+		*valp = 0;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int emulate_sys_reg(u32 id, u64 *valp)
+{
+	struct arm64_ftr_reg *regp;
+
+	if (!is_emulated(id))
+		return -EINVAL;
+
+	if (sys_reg_CRm(id) == 0)
+		return emulate_id_reg(id, valp);
+
+	regp = get_arm64_ftr_reg(id);
+	if (regp)
+		*valp = arm64_ftr_reg_user_value(regp);
+	else
+		/*
+		 * The untracked registers are either IMPLEMENTATION DEFINED
+		 * (e.g, ID_AFR0_EL1) or reserved RAZ.
+		 */
+		*valp = 0;
+	return 0;
+}
+
+static int emulate_mrs(struct pt_regs *regs, u32 insn)
+{
+	int rc;
+	u32 sys_reg, dst;
+	u64 val;
+
+	/*
+	 * sys_reg values are defined as used in mrs/msr instruction.
+	 * shift the imm value to get the encoding.
+	 */
+	sys_reg = (u32)aarch64_insn_decode_immediate(AARCH64_INSN_IMM_16, insn) << 5;
+	rc = emulate_sys_reg(sys_reg, &val);
+	if (!rc) {
+		dst = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RT, insn);
+		regs->user_regs.regs[dst] = val;
+		regs->pc += 4;
+	}
+
+	return rc;
+}
+
+static struct undef_hook mrs_hook = {
+	.instr_mask = 0xfff00000,
+	.instr_val  = 0xd5300000,
+	.pstate_mask = COMPAT_PSR_MODE_MASK,
+	.pstate_val = PSR_MODE_EL0t,
+	.fn = emulate_mrs,
+};
+
+int __init enable_mrs_emulation(void)
+{
+	register_undef_hook(&mrs_hook);
+	return 0;
+}
+
+late_initcall(enable_mrs_emulation);
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 7b7be71..4d44edd 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -63,6 +63,7 @@ static const char *const hwcap_str[] = {
 	"atomics",
 	"fphp",
 	"asimdhp",
+	"cpuid",
 	NULL
 };
 
-- 
2.7.4

[PATCH v3 9/9] arm64: Documentation - Expose CPU feature registers

[Suzuki K Poulose]

Documentation for the infrastructure to expose CPU feature
register by emulating MRS.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Dave Martin <dave.martin@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
Changes since V2:
 - Include the sample program in the documentation
---
 Documentation/arm64/cpu-feature-registers.txt | 265 ++++++++++++++++++++++++++
 arch/arm64/kernel/cpufeature.c                |   4 +
 2 files changed, 269 insertions(+)
 create mode 100644 Documentation/arm64/cpu-feature-registers.txt

diff --git a/Documentation/arm64/cpu-feature-registers.txt b/Documentation/arm64/cpu-feature-registers.txt
new file mode 100644
index 0000000..816300a
--- /dev/null
+++ b/Documentation/arm64/cpu-feature-registers.txt
@@ -0,0 +1,265 @@
+		ARM64 CPU Feature Registers
+		===========================
+
+Author: Suzuki K Poulose <suzuki.poulose@arm.com>
+
+
+This file describes the ABI for exporting the AArch64 CPU ID/feature
+registers to userspace. The availability of this ABI is advertised
+via the HWCAP_CPUID in HWCAPs.
+
+1. Motivation
+---------------
+
+The ARM architecture defines a set of feature registers, which describe
+the capabilities of the CPU/system. Access to these system registers is
+restricted from EL0 and there is no reliable way for an application to
+extract this information to make better decisions at runtime. There is
+limited information available to the application via HWCAPs, however
+there are some issues with their usage.
+
+ a) Any change to the HWCAPs requires an update to userspace (e.g libc)
+    to detect the new changes, which can take a long time to appear in
+    distributions. Exposing the registers allows applications to get the
+    information without requiring updates to the toolchains.
+
+ b) Access to HWCAPs is sometimes limited (e.g prior to libc, or
+    when ld is initialised at startup time).
+
+ c) HWCAPs cannot represent non-boolean information effectively. The
+    architecture defines a canonical format for representing features
+    in the ID registers; this is well defined and is capable of
+    representing all valid architecture variations.
+
+
+2. Requirements
+-----------------
+
+ a) Safety :
+    Applications should be able to use the information provided by the
+    infrastructure to run safely across the system. This has greater
+    implications on a system with heterogeneous CPUs.
+    The infrastructure exports a value that is safe across all the
+    available CPU on the system.
+
+    e.g, If at least one CPU doesn't implement CRC32 instructions, while
+    others do, we should report that the CRC32 is not implemented.
+    Otherwise an application could crash when scheduled on the CPU
+    which doesn't support CRC32.
+
+ b) Security :
+    Applications should only be able to receive information that is
+    relevant to the normal operation in userspace. Hence, some of the
+    fields are masked out and the values of the fields are set to
+    indicate the feature is 'not supported' (See the 'visible' field in
+    the table in Section 4). Also, the kernel may manipulate the fields
+    based on what it supports. e.g, If FP is not supported by the
+    kernel, the values could indicate that the FP is not available
+    (even when the CPU provides it).
+
+ c) Implementation Defined Features
+    The infrastructure doesn't expose any register which is
+    IMPLEMENTATION DEFINED as per ARMv8-A Architecture.
+
+ d) CPU Identification :
+    MIDR_EL1 is exposed to help identify the processor. On a
+    heterogeneous system, this could be racy (just like getcpu()). The
+    process could be migrated to another CPU by the time it uses the
+    register value, unless the CPU affinity is set. Hence, there is no
+    guarantee that the value reflects the processor that it is
+    currently executing on. The REVIDR is not exposed due to this
+    constraint, as REVIDR makes sense only in conjunction with the
+    MIDR. Alternately, MIDR_EL1 and REVIDR_EL1 are exposed via sysfs
+    at:
+
+	/sys/devices/system/cpu/cpu$ID/regs/identification/
+	                                              \- midr
+	                                              \- revidr
+
+The list of supported registers and the attributes of individual
+feature bits are listed in section 4. Unless there is absolute
+necessity, we don't encourage the addition of new feature registers to
+the list. In any case, it should comply to the requirements listed
+above.
+
+3. Implementation
+--------------------
+
+The infrastructure is built on the emulation of the 'MRS' instruction.
+Accessing a restricted system register from an application generates an
+exception and ends up in SIGILL being delivered to the process.
+The infrastructure hooks into the exception handler and emulates the
+operation if the source belongs to the supported system register space.
+
+The infrastructure emulates only the following system register space:
+	Op0=3, Op1=0, CRn=0, CRm=0,4,5,6,7
+
+(See Table C5-6 'System instruction encodings for non-Debug System
+register accesses' in ARMv8 ARM DDI 0487A.h, for the list of
+registers).
+
+
+The following rules are applied to the value returned by the
+infrastructure:
+
+ a) The value of an 'IMPLEMENTATION DEFINED' field is set to 0.
+ b) The value of a reserved field is populated with the reserved
+    value as defined by the architecture.
+ c) The value of a field marked as not 'visible', is set to indicate
+    the feature is missing (as defined by the architecture).
+ d) The value of a 'visible' field holds the system wide safe value
+    for the particular feature(except for MIDR_EL1, see section 4).
+    See Appendix I for more information on safe value.
+
+There are only a few registers visible to the userspace. See Section 4,
+for the list of 'visible' registers.
+
+All others are emulated as having 'invisible' features.
+
+4. List of exposed registers
+-----------------------------
+
+  1) ID_AA64ISAR0_EL1 - Instruction Set Attribute Register 0
+     x--------------------------------------------------x
+     | Name                         |  bits   | visible |
+     |--------------------------------------------------|
+     | RES0                         | [63-24] |    y    |
+     |--------------------------------------------------|
+     | ATOMICS                      | [20-23] |    y    |
+     |--------------------------------------------------|
+     | CRC32                        | [19-16] |    y    |
+     |--------------------------------------------------|
+     | SHA2                         | [15-12] |    y    |
+     |--------------------------------------------------|
+     | SHA1                         | [11-8]  |    y    |
+     |--------------------------------------------------|
+     | AES                          | [7-4]   |    y    |
+     |--------------------------------------------------|
+     | RES0                         | [3-0]   |    y    |
+     x--------------------------------------------------x
+
+  2) ID_AA64ISAR1_EL1 - Instruction Set Attribute Register 1
+     x--------------------------------------------------x
+     | Name                         |  bits   | visible |
+     |--------------------------------------------------|
+     | RES0                         | [63-0]  |    y    |
+     x--------------------------------------------------x
+
+  3) ID_AA64PFR0_EL1 - Processor Feature Register 0
+     x--------------------------------------------------x
+     | Name                         |  bits   | visible |
+     |--------------------------------------------------|
+     | RES0                         | [63-28] |    y    |
+     |--------------------------------------------------|
+     | GIC                          | [27-24] |    n    |
+     |--------------------------------------------------|
+     | AdvSIMD                      | [23-20] |    y    |
+     |--------------------------------------------------|
+     | FP                           | [19-16] |    y    |
+     |--------------------------------------------------|
+     | EL3                          | [15-12] |    n    |
+     |--------------------------------------------------|
+     | EL2                          | [11-8]  |    n    |
+     |--------------------------------------------------|
+     | EL1                          | [7-4]   |    n    |
+     |--------------------------------------------------|
+     | EL0                          | [3-0]   |    n    |
+     x--------------------------------------------------x
+
+  4) ID_AA64PFR1_EL1 - Processor Feature Register 1
+     x--------------------------------------------------x
+     | Name                         |  bits   | visible |
+     |--------------------------------------------------|
+     | RES0                         | [63-0]  |    y    |
+     x--------------------------------------------------x
+
+  5) MIDR_EL1 - Main ID Register
+     x--------------------------------------------------x
+     | Name                         |  bits   | visible |
+     |--------------------------------------------------|
+     | RES0                         | [63-32] |    y    |
+     |--------------------------------------------------|
+     | Implementer                  | [31-24] |    y    |
+     |--------------------------------------------------|
+     | Variant                      | [23-20] |    y    |
+     |--------------------------------------------------|
+     | Architecture                 | [19-16] |    y    |
+     |--------------------------------------------------|
+     | PartNum                      | [15-4]  |    y    |
+     |--------------------------------------------------|
+     | Revision                     | [3-0]   |    y    |
+     x--------------------------------------------------x
+
+   NOTE: The 'visible' fields of MIDR_EL1 will contain the value
+   as available on the CPU where it is fetched and is not a system
+   wide safe value.
+
+Appendix I: Example
+---------------------------
+
+/*
+ * Sample program to demonstrate the MRS emulation ABI.
+ *
+ * Copyright (C) 2015-2016, ARM Ltd
+ *
+ * Author: Suzuki K Poulose <suzuki.poulose@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <asm/hwcap.h>
+#include <stdio.h>
+#include <sys/auxv.h>
+
+#define get_cpu_ftr(id) ({					\
+		unsigned long __val;				\
+		asm("mrs %0, "#id : "=r" (__val));		\
+		printf("%-20s: 0x%016lx\n", #id, __val);	\
+	})
+
+int main(void)
+{
+
+	if (!(getauxval(AT_HWCAP) & HWCAP_CPUID)) {
+		fputs("CPUID registers unavailable\n", stderr);
+		return 1;
+	}
+
+	get_cpu_ftr(ID_AA64ISAR0_EL1);
+	get_cpu_ftr(ID_AA64ISAR1_EL1);
+	get_cpu_ftr(ID_AA64MMFR0_EL1);
+	get_cpu_ftr(ID_AA64MMFR1_EL1);
+	get_cpu_ftr(ID_AA64PFR0_EL1);
+	get_cpu_ftr(ID_AA64PFR1_EL1);
+	get_cpu_ftr(ID_AA64DFR0_EL1);
+	get_cpu_ftr(ID_AA64DFR1_EL1);
+
+	get_cpu_ftr(MIDR_EL1);
+	get_cpu_ftr(MPIDR_EL1);
+	get_cpu_ftr(REVIDR_EL1);
+
+#if 0
+	/* Unexposed register access causes SIGILL */
+	get_cpu_ftr(ID_MMFR0_EL1);
+#endif
+
+	return 0;
+}
+
+
+
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index bb635a7..3e56438 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -82,6 +82,10 @@ static bool __maybe_unused
 cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused);
 
 
+/*
+ * NOTE: Any changes to the visibility of features should be kept in
+ * sync with the documentation of the CPU feature register ABI.
+ */
 static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
-- 
2.7.4

Re: [PATCH v3 1/9] arm64: cpufeature: treat unknown fields as RES0

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:48:59PM +0000, Suzuki K. Poulose wrote:
> From: Mark Rutland <mark.rutland@arm.com>
> 
> Any fields not defined in an arm64_ftr_bits entry are propagated to the
> system-wide register value in init_cpu_ftr_reg(), and while we require
> that these strictly match for the sanity checks, we don't update them in
> update_cpu_ftr_reg().
> 
> Generally, the lack of an arm64_ftr_bits entry indicates that the bits
> are currently RES0 (as is the case for the upper 32 bits of all
> supposedly 32-bit registers).
> 
> A better default would be to use zero for the system-wide value of
> unallocated bits, making all register checking consistent, and allowing
> for subsequent simplifications to the arm64_ftr_bits arrays.
> 
> This patch updates init_cpu_ftr_reg() to treat unallocated bits as RES0
> for the purpose of the system-wide safe value. These bits will still be
> sanity checked with strict match requirements, as is currently the case.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 2/9] arm64: cpufeature: remove explicit RAZ fields

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:00PM +0000, Suzuki K. Poulose wrote:
> From: Mark Rutland <mark.rutland@arm.com>
> 
> We currently have some RAZ fields described explicitly in our
> arm64_ftr_bits arrays. These are inconsistently commented, grouped,
> and/or applied, and maintaining these is error-prone.
> 
> Luckily, we don't need these at all. We'll never need to inspect RAZ
> fields to determine feature support, and init_cpu_ftr_reg() will ensure
> that any bits without a corresponding arm64_ftr_bits entry are treated
> as RES0 with strict matching requirements. In check_update_ftr_reg()
> we'll then compare these bits from the relevant cpuinfo_arm64
> structures, and need not store them in a arm64_ftr_reg.
> 
> This patch removes the unnecessary arm64_ftr_bits entries for RES0 bits.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 3/9] arm64: cpufeature: Cleanup feature bit tables

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:01PM +0000, Suzuki K. Poulose wrote:
> This patch does the following clean ups :
> 
> 1) All undescribed fields of a register are now treated as "strict"
>    with a safe value of 0. Hence we could leave an empty table for
>    describing registers which are RAZ.
> 
> 2) ID_AA64DFR1_EL1 is RAZ and should use the table for RAZ register.
> 
> 3) ftr_generic32 is used to represent a register with a 32bit feature
>    value. Rename this to ftr_singl32 to make it more obvious. Since
>    we don't have a 64bit singe feature register, kill ftr_generic.

Nitpick: couple of "single" typos above.

> 
> Based on a patch by Mark Rutland.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 5/9] arm64: cpufeature: Define helpers for sys_reg id

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:03PM +0000, Suzuki K. Poulose wrote:
> Define helper macros to extract op0, op1, CRn, CRm & op2
> for a given sys_reg id. While at it remove the explicit
> masking only used for Op0.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 6/9] arm64: Add helper to decode register from instruction

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:04PM +0000, Suzuki K. Poulose wrote:
> Add a helper to extract the register field from a given
> instruction.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 7/9] arm64: cpufeature: Track user visible fields

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:05PM +0000, Suzuki K. Poulose wrote:
> Track the user visible fields of a CPU feature register. This will be
> used for exposing the value to the userspace. All the user visible
> fields of a feature register will be passed on as it is, while the
> others would be filled with their respective safe value.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

> @@ -81,75 +82,75 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
>  
>  
>  static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
> -	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),

BTW, as a separate patch I think we need to expose the RDM field in this
register as well, together with a corresponding HWCAP bit.

-- 
Catalin

Re: [PATCH v3 8/9] arm64: cpufeature: Expose CPUID registers by emulation

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:06PM +0000, Suzuki K. Poulose wrote:
> This patch adds the hook for emulating MRS instruction to
> export the 'user visible' value of supported system registers.
> We emulate only the following id space for system registers:
> 
>  Op0=3, Op1=0, CRn=0, CRm=[0, 4-7]
> 
> The rest will fall back to SIGILL. This capability is also
> advertised via a new HWCAP_CPUID.
> 
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 7/9] arm64: cpufeature: Track user visible fields

[Suzuki K Poulose]

On 05/01/17 18:06, Catalin Marinas wrote:
> On Wed, Jan 04, 2017 at 05:49:05PM +0000, Suzuki K. Poulose wrote:
>> Track the user visible fields of a CPU feature register. This will be
>> used for exposing the value to the userspace. All the user visible
>> fields of a feature register will be passed on as it is, while the
>> others would be filled with their respective safe value.
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>
>> @@ -81,75 +82,75 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
>>
>>
>>  static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
>> -	ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),
>> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
>> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
>> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
>> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
>> -	ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),
>> +	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64ISAR0_RDM_SHIFT, 4, 0),

On a second look, I think we should make the RDM field visible to the user space as it
is something useful for the user.

>> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_ATOMICS_SHIFT, 4, 0),
>> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_CRC32_SHIFT, 4, 0),
>> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA2_SHIFT, 4, 0),
>> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_SHA1_SHIFT, 4, 0),
>> +	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_AES_SHIFT, 4, 0),
>
> BTW, as a separate patch I think we need to expose the RDM field in this
> register as well, together with a corresponding HWCAP bit.

OK, I will send a separate patch for this.

Thanks for the review.

Suzuki

Re: [PATCH v3 9/9] arm64: Documentation - Expose CPU feature registers

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:07PM +0000, Suzuki K. Poulose wrote:
> +The following rules are applied to the value returned by the
> +infrastructure:
> +
> + a) The value of an 'IMPLEMENTATION DEFINED' field is set to 0.
> + b) The value of a reserved field is populated with the reserved
> +    value as defined by the architecture.
> + c) The value of a field marked as not 'visible', is set to indicate
> +    the feature is missing (as defined by the architecture).
> + d) The value of a 'visible' field holds the system wide safe value
> +    for the particular feature(except for MIDR_EL1, see section 4).
> +    See Appendix I for more information on safe value.
> +
> +There are only a few registers visible to the userspace. See Section 4,
> +for the list of 'visible' registers.
> +
> +All others are emulated as having 'invisible' features.

BTW, we don't have any statement about whether a visible field may
become invisible but I guess this wouldn't be a problem as long as the
feature is reported as missing. I'm thinking about currently RES0 fields
that are listed as visible but they may report something in the future
that we don't want exposed to user. At that point, we'll change the
field to "invisible" while reporting RES0 to user. I don't see an issue
with this, just I thought worth flagging.

Anyway:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Re: [PATCH v3 4/9] arm64: cpufeature: Document the rules of safe value for features

[Catalin Marinas]

On Wed, Jan 04, 2017 at 05:49:02PM +0000, Suzuki K. Poulose wrote:
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -29,7 +29,21 @@
>  #include <linux/jump_label.h>
>  #include <linux/kernel.h>
>  
> -/* CPU feature register tracking */
> +/*
> + * CPU feature register tracking
> + *
> + * The safe value of a CPUID feature field is dependent on the implications
> + * of the values assigned to it by the architecture. Based on the relationship
> + * between the values, the features are classified into 3 types.
> + *
> + * a) LOWER_SAFE - The value 'n+1' indicates, value 'n' and some
> + *    additional features. (where n >= 0). The smaller value (n) is
> + *    considered safer in this case.
> + * b) HIGHER_SAFE - The value 'n+1' is safer than 'n' (for n>= 0).
> + * c) EXACT - If the values of the feature don't have any relationship,
> + *    a predefined safe value is used.
> + */

I don't think this text fully describes what is actually compared. You
could say something that the lowest value of all the CPUs is chosen for
LOWER_SAFE, highest for HIGHER_SAFE and it is expected that all CPUs
have the same value for a field when EXACT is specified.

-- 
Catalin

Re: [PATCH v3 4/9] arm64: cpufeature: Document the rules of safe value for features

[Suzuki K Poulose]

On 06/01/17 12:30, Catalin Marinas wrote:
> On Wed, Jan 04, 2017 at 05:49:02PM +0000, Suzuki K. Poulose wrote:
>> --- a/arch/arm64/include/asm/cpufeature.h
>> +++ b/arch/arm64/include/asm/cpufeature.h
>> @@ -29,7 +29,21 @@
>>  #include <linux/jump_label.h>
>>  #include <linux/kernel.h>
>>
>> -/* CPU feature register tracking */
>> +/*
>> + * CPU feature register tracking
>> + *
>> + * The safe value of a CPUID feature field is dependent on the implications
>> + * of the values assigned to it by the architecture. Based on the relationship
>> + * between the values, the features are classified into 3 types.
>> + *
>> + * a) LOWER_SAFE - The value 'n+1' indicates, value 'n' and some
>> + *    additional features. (where n >= 0). The smaller value (n) is
>> + *    considered safer in this case.
>> + * b) HIGHER_SAFE - The value 'n+1' is safer than 'n' (for n>= 0).
>> + * c) EXACT - If the values of the feature don't have any relationship,
>> + *    a predefined safe value is used.
>> + */
>
> I don't think this text fully describes what is actually compared. You
> could say something that the lowest value of all the CPUs is chosen for
> LOWER_SAFE, highest for HIGHER_SAFE and it is expected that all CPUs
> have the same value for a field when EXACT is specified.

Ok. I have changed it as below :

/*
  * CPU feature register tracking
  *
  * The safe value of a CPUID feature field is dependent on the implications
  * of the values assigned to it by the architecture. Based on the relationship
  * between the values, the features are classified into 3 types - LOWER_SAFE,
  * HIGHER_SAFE and EXACT.
  *
  * The lowest value of all the CPUs is chosen for LOWER_SAFE and highest
  * for HIGHER_SAFE. It is expected that all CPUs have the same value for
  * a field when EXACT is specified, failing which, the safe value specified
  * in the table is chosen.
  */


Suzuki

Re: [PATCH v3 9/9] arm64: Documentation - Expose CPU feature registers

[Suzuki K Poulose]

On 06/01/17 12:16, Catalin Marinas wrote:
> On Wed, Jan 04, 2017 at 05:49:07PM +0000, Suzuki K. Poulose wrote:
>> +The following rules are applied to the value returned by the
>> +infrastructure:
>> +
>> + a) The value of an 'IMPLEMENTATION DEFINED' field is set to 0.
>> + b) The value of a reserved field is populated with the reserved
>> +    value as defined by the architecture.
>> + c) The value of a field marked as not 'visible', is set to indicate
>> +    the feature is missing (as defined by the architecture).
>> + d) The value of a 'visible' field holds the system wide safe value
>> +    for the particular feature(except for MIDR_EL1, see section 4).
>> +    See Appendix I for more information on safe value.
>> +
>> +There are only a few registers visible to the userspace. See Section 4,
>> +for the list of 'visible' registers.
>> +
>> +All others are emulated as having 'invisible' features.
>
> BTW, we don't have any statement about whether a visible field may
> become invisible but I guess this wouldn't be a problem as long as the
> feature is reported as missing. I'm thinking about currently RES0 fields
> that are listed as visible but they may report something in the future
> that we don't want exposed to user. At that point, we'll change the
> field to "invisible" while reporting RES0 to user. I don't see an issue
> with this, just I thought worth flagging.

Thanks for raising that. In fact, we treat all the RES0 fields as invisible
and strict for the moment. So, I think it is worth reflecting that in the
documentation. As you mentioned, we could switch them as required based on
the feature without any issues. I will fix this.

>
> Anyway:
>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>

Thanks for reviewing the entire series. I will resend the series with the tags
and updates to this documentation and a couple of other patches.

Suzuki

Re: [PATCH v3 4/9] arm64: cpufeature: Document the rules of safe value for features

[Catalin Marinas]

On Mon, Jan 09, 2017 at 10:43:07AM +0000, Suzuki K. Poulose wrote:
> On 06/01/17 12:30, Catalin Marinas wrote:
> >On Wed, Jan 04, 2017 at 05:49:02PM +0000, Suzuki K. Poulose wrote:
> >>--- a/arch/arm64/include/asm/cpufeature.h
> >>+++ b/arch/arm64/include/asm/cpufeature.h
> >>@@ -29,7 +29,21 @@
> >> #include <linux/jump_label.h>
> >> #include <linux/kernel.h>
> >>
> >>-/* CPU feature register tracking */
> >>+/*
> >>+ * CPU feature register tracking
> >>+ *
> >>+ * The safe value of a CPUID feature field is dependent on the implications
> >>+ * of the values assigned to it by the architecture. Based on the relationship
> >>+ * between the values, the features are classified into 3 types.
> >>+ *
> >>+ * a) LOWER_SAFE - The value 'n+1' indicates, value 'n' and some
> >>+ *    additional features. (where n >= 0). The smaller value (n) is
> >>+ *    considered safer in this case.
> >>+ * b) HIGHER_SAFE - The value 'n+1' is safer than 'n' (for n>= 0).
> >>+ * c) EXACT - If the values of the feature don't have any relationship,
> >>+ *    a predefined safe value is used.
> >>+ */
> >
> >I don't think this text fully describes what is actually compared. You
> >could say something that the lowest value of all the CPUs is chosen for
> >LOWER_SAFE, highest for HIGHER_SAFE and it is expected that all CPUs
> >have the same value for a field when EXACT is specified.
> 
> Ok. I have changed it as below :
> 
> /*
>  * CPU feature register tracking
>  *
>  * The safe value of a CPUID feature field is dependent on the implications
>  * of the values assigned to it by the architecture. Based on the relationship
>  * between the values, the features are classified into 3 types - LOWER_SAFE,
>  * HIGHER_SAFE and EXACT.
>  *
>  * The lowest value of all the CPUs is chosen for LOWER_SAFE and highest
>  * for HIGHER_SAFE. It is expected that all CPUs have the same value for
>  * a field when EXACT is specified, failing which, the safe value specified
>  * in the table is chosen.
>  */

It looks better to me. Thanks.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>