arm64/cpufeatures: Emulate MRS instructions by parsing ESR_ELx.ISS

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

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index cc2d9e7..37e84f2 100644 (file)
--- 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 abfb304..21689c6 100644 (file)
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -497,6 +497,17 @@ 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;
@@ -527,6 +538,12 @@ 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,
+       },
        {},
 };