[PATCH v2 8/9] arm64: cpufeature: Expose CPUID registers by emulation
From: Suzuki K Poulose
Date: Wed Nov 30 2016 - 10:17:25 EST
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.marinas@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
---
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