[PATCH V2 0/3] Emulate MRS instructions by parsing ESR_ELx.ISS

[PATCH V2 0/3] Emulate MRS instructions by parsing ESR_ELx.ISS

[Anshuman Khandual]

Armv8.4-A extension enables MRS instruction encodings inside ESR_ELx.ISS
during exception class ESR_ELx_EC_SYS64 (0x18). This encoding can be used
to emulate MRS instructions which can avoid fetch/decode from user space
thus improving performance. The patch series here enables this new method
of emulating MRS instruction. For this purpose we factorizes the existing
emulate_mrs() function and while here, add new macro ESR_ELx_SYS64_ISS_RT.

Changes in V2:

- Replaced the argument 'dst' as 'rt' in second patch per Suzuki
- Added review tags from Suzuki

Anshuman Khandual (3):
  arm64/cpufeatures: Introduce ESR_ELx_SYS64_ISS_RT()
  arm64/cpufeatures: Factorize emulate_mrs()
  arm64/cpufeatures: Emulate MRS instructions by parsing ESR_ELx.ISS

 arch/arm64/include/asm/cpufeature.h  |  1 +
 arch/arm64/include/asm/esr.h         | 14 ++++++++++++++
 arch/arm64/include/asm/kvm_emulate.h |  2 +-
 arch/arm64/kernel/cpufeature.c       | 25 +++++++++++++++----------
 arch/arm64/kernel/traps.c            | 25 +++++++++++++++++++++----
 5 files changed, 52 insertions(+), 15 deletions(-)

-- 
2.7.4

[PATCH V2 1/3] arm64/cpufeatures: Introduce ESR_ELx_SYS64_ISS_RT()

[Anshuman Khandual]

Extracting target register from ESR.ISS encoding has already been required
at multiple instances. Just make it a macro definition and replace all the
existing use cases.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/include/asm/esr.h         | 2 ++
 arch/arm64/include/asm/kvm_emulate.h | 2 +-
 arch/arm64/kernel/traps.c            | 8 ++++----
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index ce70c3f..cc2d9e7 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -187,6 +187,8 @@
 
 #define ESR_ELx_SYS64_ISS_SYS_OP_MASK	(ESR_ELx_SYS64_ISS_SYS_MASK | \
 					 ESR_ELx_SYS64_ISS_DIR_MASK)
+#define ESR_ELx_SYS64_ISS_RT(esr) \
+	(((esr) & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT)
 /*
  * User space cache operations have the following sysreg encoding
  * in System instructions.
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 6106a85..2124787 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -335,7 +335,7 @@ static inline bool kvm_vcpu_dabt_isextabt(const struct kvm_vcpu *vcpu)
 static inline int kvm_vcpu_sys_get_rt(struct kvm_vcpu *vcpu)
 {
 	u32 esr = kvm_vcpu_get_hsr(vcpu);
-	return (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+	return ESR_ELx_SYS64_ISS_RT(esr);
 }
 
 static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 039e9ff..15276b2 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -437,7 +437,7 @@ void cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
 static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
 {
 	unsigned long address;
-	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+	int rt = ESR_ELx_SYS64_ISS_RT(esr);
 	int crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT;
 	int ret = 0;
 
@@ -472,7 +472,7 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
 
 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;
+	int rt = ESR_ELx_SYS64_ISS_RT(esr);
 	unsigned long val = arm64_ftr_reg_user_value(&arm64_ftr_reg_ctrel0);
 
 	pt_regs_write_reg(regs, rt, val);
@@ -482,7 +482,7 @@ static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
 
 static void cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
 {
-	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+	int rt = ESR_ELx_SYS64_ISS_RT(esr);
 
 	pt_regs_write_reg(regs, rt, arch_counter_get_cntvct());
 	arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
@@ -490,7 +490,7 @@ static void cntvct_read_handler(unsigned int esr, struct pt_regs *regs)
 
 static void cntfrq_read_handler(unsigned int esr, struct pt_regs *regs)
 {
-	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+	int rt = ESR_ELx_SYS64_ISS_RT(esr);
 
 	pt_regs_write_reg(regs, rt, arch_timer_get_rate());
 	arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
-- 
2.7.4

[PATCH V2 2/3] arm64/cpufeatures: Factorize emulate_mrs()

[Anshuman Khandual]

MRS emulation gets triggered with exception class (0x00 or 0x18) eventually
calling the function emulate_mrs() which fetches the user space instruction
and analyses it's encodings (OP0, OP1, OP2, CRN, CRM, RT). The kernel tries
to emulate the given instruction looking into the encoding details. Going
forward these encodings can also be parsed from ESR_ELx.ISS fields without
requiring to fetch/decode faulting userspace instruction which can improve
performance. This factorizes emulate_mrs() function in a way that it can be
called directly with MRS encodings (OP0, OP1, OP2, CRN, CRM) for any given
target register which can then be used directly from 0x18 exception class.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/include/asm/cpufeature.h |  1 +
 arch/arm64/kernel/cpufeature.c      | 25 +++++++++++++++----------
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 1717ba1..7fcaaa4 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -530,6 +530,7 @@ void arm64_set_ssbd_mitigation(bool state);
 static inline void arm64_set_ssbd_mitigation(bool state) {}
 #endif
 
+extern int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 #endif /* __ASSEMBLY__ */
 
 #endif
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index e238b79..6126583 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1719,27 +1719,32 @@ static int emulate_sys_reg(u32 id, u64 *valp)
 	return 0;
 }
 
-static int emulate_mrs(struct pt_regs *regs, u32 insn)
+int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt)
 {
 	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);
-		pt_regs_write_reg(regs, dst, val);
+		pt_regs_write_reg(regs, rt, val);
 		arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
 	}
-
 	return rc;
 }
 
+static int emulate_mrs(struct pt_regs *regs, u32 insn)
+{
+	u32 sys_reg, rt;
+
+	/*
+	 * 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;
+	rt = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RT, insn);
+	return do_emulate_mrs(regs, sys_reg, rt);
+}
+
 static struct undef_hook mrs_hook = {
 	.instr_mask = 0xfff00000,
 	.instr_val  = 0xd5300000,
-- 
2.7.4

[PATCH V2 3/3] arm64/cpufeatures: Emulate MRS instructions by parsing ESR_ELx.ISS

[Anshuman Khandual]

Armv8.4-A extension enables MRS instruction encodings inside ESR_ELx.ISS
during exception class ESR_ELx_EC_SYS64 (0x18). This encoding can be used
to emulate MRS instructions which can avoid fetch/decode from user space
thus improving performance. This adds a new sys64_hook structure element
with applicable ESR mask/value pair for MRS instructions on various system
registers but constrained by sysreg encodings which is currently allowed
to be emulated.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
 arch/arm64/include/asm/esr.h | 12 ++++++++++++
 arch/arm64/kernel/traps.c    | 17 +++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index cc2d9e7..37e84f2 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -208,6 +208,18 @@
 #define ESR_ELx_SYS64_ISS_EL0_CACHE_OP_VAL \
 				(ESR_ELx_SYS64_ISS_SYS_VAL(1, 3, 1, 7, 0) | \
 				 ESR_ELx_SYS64_ISS_DIR_WRITE)
+/*
+ * User space MRS operations which are supported for emulation
+ * have the following sysreg encoding in System instructions.
+ * op0 = 3, op1= 0, crn = 0, {crm = 0, 4-7}, READ (L = 1)
+ */
+#define ESR_ELx_SYS64_ISS_SYS_MRS_OP_MASK	(ESR_ELx_SYS64_ISS_OP0_MASK | \
+						 ESR_ELx_SYS64_ISS_OP1_MASK | \
+						 ESR_ELx_SYS64_ISS_CRN_MASK | \
+						 ESR_ELx_SYS64_ISS_DIR_MASK)
+#define ESR_ELx_SYS64_ISS_SYS_MRS_OP_VAL \
+				(ESR_ELx_SYS64_ISS_SYS_VAL(3, 0, 0, 0, 0) | \
+				 ESR_ELx_SYS64_ISS_DIR_READ)
 
 #define ESR_ELx_SYS64_ISS_SYS_CTR	ESR_ELx_SYS64_ISS_SYS_VAL(3, 3, 1, 0, 0)
 #define ESR_ELx_SYS64_ISS_SYS_CTR_READ	(ESR_ELx_SYS64_ISS_SYS_CTR | \
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 15276b2..3a2e61b 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -496,6 +496,17 @@ static void cntfrq_read_handler(unsigned int esr, struct pt_regs *regs)
 	arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
 }
 
+static void mrs_handler(unsigned int esr, struct pt_regs *regs)
+{
+	u32 sysreg, rt;
+
+	rt = ESR_ELx_SYS64_ISS_RT(esr);
+	sysreg = esr_sys64_to_sysreg(esr);
+
+	if (do_emulate_mrs(regs, sysreg, rt) != 0)
+		force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc);
+}
+
 struct sys64_hook {
 	unsigned int esr_mask;
 	unsigned int esr_val;
@@ -526,6 +537,12 @@ static struct sys64_hook sys64_hooks[] = {
 		.esr_val = ESR_ELx_SYS64_ISS_SYS_CNTFRQ,
 		.handler = cntfrq_read_handler,
 	},
+	{
+		/* Trap read access to CPUID registers */
+		.esr_mask = ESR_ELx_SYS64_ISS_SYS_MRS_OP_MASK,
+		.esr_val = ESR_ELx_SYS64_ISS_SYS_MRS_OP_VAL,
+		.handler = mrs_handler,
+	},
 	{},
 };
 
-- 
2.7.4

[PATCH V2 0/3] Emulate MRS instructions by parsing ESR_ELx.ISS

[Catalin Marinas]

On Thu, Sep 20, 2018 at 09:36:18AM +0530, Anshuman Khandual wrote:
> Armv8.4-A extension enables MRS instruction encodings inside ESR_ELx.ISS
> during exception class ESR_ELx_EC_SYS64 (0x18). This encoding can be used
> to emulate MRS instructions which can avoid fetch/decode from user space
> thus improving performance. The patch series here enables this new method
> of emulating MRS instruction. For this purpose we factorizes the existing
> emulate_mrs() function and while here, add new macro ESR_ELx_SYS64_ISS_RT.
> 
> Changes in V2:
> 
> - Replaced the argument 'dst' as 'rt' in second patch per Suzuki
> - Added review tags from Suzuki
> 
> Anshuman Khandual (3):
>   arm64/cpufeatures: Introduce ESR_ELx_SYS64_ISS_RT()
>   arm64/cpufeatures: Factorize emulate_mrs()
>   arm64/cpufeatures: Emulate MRS instructions by parsing ESR_ELx.ISS

Queued for 4.20. Thanks.

-- 
Catalin