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.mari...@arm.com> Cc: Mark Rutland <mark.rutl...@arm.com> Cc: Will Deacon <will.dea...@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poul...@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 c94a56f..7d00ce21 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -239,6 +239,10 @@ #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 a7532dd..fa52042 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; @@ -916,6 +917,8 @@ 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); @@ -1103,3 +1106,101 @@ cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused) { return (cpus_have_cap(ARM64_HAS_PAN) && !cpus_have_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 b3d5b3e..ef8406f 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