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/kernel/traps.c b/arch/arm64/kernel/traps.c
index abfb304..21689c6 100644
--- 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,
+ },
{},
};