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Date: Mon, 5 Oct 2015 18:02:09 +0100
From: "Suzuki K. Poulose" <suzuki.poulose@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: marc.zyngier@....com, will.deacon@....com, mark.rutland@....com,
catalin.marinas@....com, steve.capper@...aro.org,
linux-kernel@...r.kernel.org, andre.przywara@....com,
dave.martin@....com, Vladimir.Murzin@....com, james.morse@....com,
ard.biesheuvel@...aro.org, edward.nevill@...aro.org,
aph@...hat.com, "Suzuki K. Poulose" <suzuki.poulose@....com>
Subject: [PATCH v2 20/22] arm64: Expose feature registers by emulating MRS
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=0, Op1=0, CRn=0.
The rest will fall back to SIGILL.
This capability is also advertised via a new HWCAP_CPUID.
Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
---
arch/arm64/include/asm/sysreg.h | 3 ++
arch/arm64/include/uapi/asm/hwcap.h | 1 +
arch/arm64/kernel/cpufeature.c | 95 +++++++++++++++++++++++++++++++++++
arch/arm64/kernel/cpuinfo.c | 1 +
4 files changed, 100 insertions(+)
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index dc72fc6..b44ad93 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -192,6 +192,9 @@
#define MVFR1_FPFTZ_SHIFT 0
+/* Safe value for MPIDR_EL1: Bit31:RES1, Bit30:U:0, Bit24:MT:1 */
+#define SYS_MPIDR_SAFE_VAL ((1UL<<31)|(1UL<<24))
+
#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 361c8a8..3386e64 100644
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/arch/arm64/include/uapi/asm/hwcap.h
@@ -28,5 +28,6 @@
#define HWCAP_SHA2 (1 << 6)
#define HWCAP_CRC32 (1 << 7)
#define HWCAP_ATOMICS (1 << 8)
+#define HWCAP_CPUID (1 << 9)
#endif /* _UAPI__ASM_HWCAP_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f8fee51..54a8f2e 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -24,6 +24,7 @@
#include <asm/cpufeature.h>
#include <asm/processor.h>
#include <asm/sysreg.h>
+#include <asm/traps.h>
unsigned long elf_hwcap __read_mostly;
EXPORT_SYMBOL_GPL(elf_hwcap);
@@ -710,6 +711,8 @@ void check_cpu_hwcaps(void)
{
int i;
const struct arm64_cpu_capabilities *hwcaps = arm64_hwcaps;
+
+ elf_hwcap |= HWCAP_CPUID;
for(i = 0; i < ARRAY_SIZE(arm64_hwcaps); i ++)
if (hwcaps[i].matches(&hwcaps[i]))
cap_set_hwcap(&hwcaps[i]);
@@ -880,3 +883,95 @@ void __init setup_cpu_features(void)
pr_warn("L1_CACHE_BYTES smaller than the Cache Writeback Granule (%d < %d)\n",
L1_CACHE_BYTES, cls);
}
+
+/*
+ * We emulate only the following system register space.
+ * Op0 = 0x3, CRn = 0x0, Op1 = 0x0
+ * See Table C5-6 System instruction encodings for System register accesses,
+ * ARMv8 ARM(ARM DDI 0487A.f) for more details.
+ */
+static int __attribute_const__ is_emulated(u32 id)
+{
+ if (sys_reg_Op0(id) != 0x3 ||
+ sys_reg_CRn(id) != 0x0 ||
+ sys_reg_Op1(id) != 0x0)
+ return 0;
+ return 1;
+}
+
+/*
+ * With CRm = 0, id should be one of :
+ * MIDR_EL1
+ * MPIDR_EL1
+ * REVIDR_EL1
+ */
+static int emulate_id_reg(u32 id, u64 *valp)
+{
+ switch(id) {
+ case SYS_MIDR_EL1:
+ *valp = read_cpuid_id();
+ return 0;
+ case SYS_MPIDR_EL1:
+ *valp = SYS_MPIDR_SAFE_VAL;
+ return 0;
+ case SYS_REVIDR_EL1:
+ *valp = 0;
+ return 0;
+ default:
+ return -EINVAL;
+ }
+}
+
+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_sys_reg(id);
+ if (regp)
+ *valp = regp->user_val | (regp->sys_val & regp->user_mask);
+ else
+ /*
+ * Registers we don't track are either IMPLEMENTAION 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 = 0;
+ u32 sys_reg, dst;
+ u64 val = 0;
+
+ sys_reg = (u32)aarch64_insn_decode_immediate(AARCH64_INSN_IMM_16, insn);
+ rc = emulate_sys_reg(sys_reg, &val);
+ if (rc)
+ return rc;
+ dst = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RT ,insn);
+ regs->user_regs.regs[dst] = val;
+ regs->pc += 4;
+ return 0;
+}
+
+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 arm64_cpufeature_init(void)
+{
+ register_undef_hook(&mrs_hook);
+ return 0;
+}
+
+late_initcall(arm64_cpufeature_init);
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index 789fbea..52331ff 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -58,6 +58,7 @@ static const char *hwcap_str[] = {
"sha2",
"crc32",
"atomics",
+ "cpuid",
NULL
};
--
1.7.9.5
--
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