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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>
This commit is contained in:
Anshuman Khandual 2018-09-20 09:36:21 +05:30 committed by Catalin Marinas
parent 520ad98871
commit 21f8479617
2 changed files with 29 additions and 0 deletions
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12
arch/arm64/include/asm/esr.h
View File

@ -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 | \

17
arch/arm64/kernel/traps.c
View File

@ -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,
},
{},
};