MIPS: Respect the ISA level in FCSR handling

Define the central place the default FCSR value is set from, initialised
in `cpu_probe'.  Determine the FCSR mask applied to values written to
the register with CTC1 in the full emulation mode and via ptrace(2),
according to the ISA level of processor hardware or the writability of
bits 31:18 if actual FPU hardware is used.

Software may rely on FCSR bits whose functions our emulator does not
implement, so it should not allow them to be set or software may get
confused.  For ptrace(2) it's just sanity.

[ralf@linux-mips.org: Fixed double inclusion of <asm/current.h>.]

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9711/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

10 files changed, 83 insertions, 21 deletions

diff --git a/arch/mips/include/asm/cpu-info.h b/arch/mips/include/asm/cpu-info.h
index c3f4f2d2e108..e7dc785a91ca 100644
--- a/arch/mips/include/asm/cpu-info.h
+++ b/arch/mips/include/asm/cpu-info.h
@@ -49,6 +49,8 @@ struct cpuinfo_mips {
 	unsigned int		udelay_val;
 	unsigned int		processor_id;
 	unsigned int		fpu_id;
+	unsigned int		fpu_csr31;
+	unsigned int		fpu_msk31;
 	unsigned int		msa_id;
 	unsigned int		cputype;
 	int			isa_level;
diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index 535f196ffe02..612cf519bd88 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -11,6 +11,9 @@
 #include <linux/fs.h>
 #include <uapi/linux/elf.h>
 
+#include <asm/cpu-info.h>
+#include <asm/current.h>
+
 /* ELF header e_flags defines. */
 /* MIPS architecture level. */
 #define EF_MIPS_ARCH_1		0x00000000	/* -mips1 code.	 */
@@ -297,6 +300,8 @@ do {									\
 	mips_set_personality_fp(state);					\
 									\
 	current->thread.abi = &mips_abi;				\
+									\
+	current->thread.fpu.fcr31 = current_cpu_data.fpu_csr31;		\
 } while (0)
 
 #endif /* CONFIG_32BIT */
@@ -356,6 +361,8 @@ do {									\
 	else								\
 		current->thread.abi = &mips_abi;			\
 									\
+	current->thread.fpu.fcr31 = current_cpu_data.fpu_csr31;		\
+									\
 	p = personality(current->personality);				\
 	if (p != PER_LINUX32 && p != PER_LINUX)				\
 		set_personality(PER_LINUX);				\
diff --git a/arch/mips/include/asm/fpu.h b/arch/mips/include/asm/fpu.h
index dd083e999b08..83d50d563a0f 100644
--- a/arch/mips/include/asm/fpu.h
+++ b/arch/mips/include/asm/fpu.h
@@ -30,7 +30,7 @@
 struct sigcontext;
 struct sigcontext32;
 
-extern void _init_fpu(void);
+extern void _init_fpu(unsigned int);
 extern void _save_fp(struct task_struct *);
 extern void _restore_fp(struct task_struct *);
 
@@ -182,6 +182,7 @@ static inline void lose_fpu(int save)
 
 static inline int init_fpu(void)
 {
+	unsigned int fcr31 = current->thread.fpu.fcr31;
 	int ret = 0;
 
 	if (cpu_has_fpu) {
@@ -192,7 +193,7 @@ static inline int init_fpu(void)
 			return ret;
 
 		if (!cpu_has_fre) {
-			_init_fpu();
+			_init_fpu(fcr31);
 
 			return 0;
 		}
@@ -206,7 +207,7 @@ static inline int init_fpu(void)
 		config5 = clear_c0_config5(MIPS_CONF5_FRE);
 		enable_fpu_hazard();
 
-		_init_fpu();
+		_init_fpu(fcr31);
 
 		/* Restore FRE */
 		write_c0_config5(config5);
diff --git a/arch/mips/include/asm/fpu_emulator.h b/arch/mips/include/asm/fpu_emulator.h
index bfcc5c64b7b0..2f021cdfba4f 100644
--- a/arch/mips/include/asm/fpu_emulator.h
+++ b/arch/mips/include/asm/fpu_emulator.h
@@ -88,8 +88,6 @@ static inline void fpu_emulator_init_fpu(void)
 	struct task_struct *t = current;
 	int i;
 
-	t->thread.fpu.fcr31 = 0;
-
 	for (i = 0; i < 32; i++)
 		set_fpr64(&t->thread.fpu.fpr[i], 0, SIGNALLING_NAN);
 }
diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c
index ca9b9c62c6ea..2911ad5977d7 100644
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -33,6 +33,35 @@
 #include <asm/uaccess.h>
 
 /*
+ * Determine the FCSR mask for FPU hardware.
+ */
+static inline void cpu_set_fpu_fcsr_mask(struct cpuinfo_mips *c)
+{
+	unsigned long sr, mask, fcsr, fcsr0, fcsr1;
+
+	mask = FPU_CSR_ALL_X | FPU_CSR_ALL_E | FPU_CSR_ALL_S | FPU_CSR_RM;
+
+	sr = read_c0_status();
+	__enable_fpu(FPU_AS_IS);
+
+	fcsr = read_32bit_cp1_register(CP1_STATUS);
+
+	fcsr0 = fcsr & mask;
+	write_32bit_cp1_register(CP1_STATUS, fcsr0);
+	fcsr0 = read_32bit_cp1_register(CP1_STATUS);
+
+	fcsr1 = fcsr | ~mask;
+	write_32bit_cp1_register(CP1_STATUS, fcsr1);
+	fcsr1 = read_32bit_cp1_register(CP1_STATUS);
+
+	write_32bit_cp1_register(CP1_STATUS, fcsr);
+
+	write_c0_status(sr);
+
+	c->fpu_msk31 = ~(fcsr0 ^ fcsr1) & ~mask;
+}
+
+/*
  * Set the FIR feature flags for the FPU emulator.
  */
 static void cpu_set_nofpu_id(struct cpuinfo_mips *c)
@@ -50,11 +79,15 @@ static void cpu_set_nofpu_id(struct cpuinfo_mips *c)
 	c->fpu_id = value;
 }
 
+/* Determined FPU emulator mask to use for the boot CPU with "nofpu".  */
+static unsigned int mips_nofpu_msk31;
+
 static int mips_fpu_disabled;
 
 static int __init fpu_disable(char *s)
 {
 	boot_cpu_data.options &= ~MIPS_CPU_FPU;
+	boot_cpu_data.fpu_msk31 = mips_nofpu_msk31;
 	cpu_set_nofpu_id(&boot_cpu_data);
 	mips_fpu_disabled = 1;
 
@@ -597,6 +630,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 	case PRID_IMP_R2000:
 		c->cputype = CPU_R2000;
 		__cpu_name[cpu] = "R2000";
+		c->fpu_msk31 |= FPU_CSR_CONDX | FPU_CSR_FS;
 		c->options = MIPS_CPU_TLB | MIPS_CPU_3K_CACHE |
 			     MIPS_CPU_NOFPUEX;
 		if (__cpu_has_fpu())
@@ -616,6 +650,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 			c->cputype = CPU_R3000;
 			__cpu_name[cpu] = "R3000";
 		}
+		c->fpu_msk31 |= FPU_CSR_CONDX | FPU_CSR_FS;
 		c->options = MIPS_CPU_TLB | MIPS_CPU_3K_CACHE |
 			     MIPS_CPU_NOFPUEX;
 		if (__cpu_has_fpu())
@@ -664,6 +699,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		}
 
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS | MIPS_CPU_FPU | MIPS_CPU_32FPR |
 			     MIPS_CPU_WATCH | MIPS_CPU_VCE |
 			     MIPS_CPU_LLSC;
@@ -671,6 +707,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		break;
 	case PRID_IMP_VR41XX:
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS;
 		c->tlbsize = 32;
 		switch (c->processor_id & 0xf0) {
@@ -712,6 +749,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_R4300;
 		__cpu_name[cpu] = "R4300";
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS | MIPS_CPU_FPU | MIPS_CPU_32FPR |
 			     MIPS_CPU_LLSC;
 		c->tlbsize = 32;
@@ -720,6 +758,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_R4600;
 		__cpu_name[cpu] = "R4600";
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS | MIPS_CPU_FPU | MIPS_CPU_32FPR |
 			     MIPS_CPU_LLSC;
 		c->tlbsize = 48;
@@ -735,11 +774,13 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_R4650;
 		__cpu_name[cpu] = "R4650";
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS | MIPS_CPU_FPU | MIPS_CPU_LLSC;
 		c->tlbsize = 48;
 		break;
 	#endif
 	case PRID_IMP_TX39:
+		c->fpu_msk31 |= FPU_CSR_CONDX | FPU_CSR_FS;
 		c->options = MIPS_CPU_TLB | MIPS_CPU_TX39_CACHE;
 
 		if ((c->processor_id & 0xf0) == (PRID_REV_TX3927 & 0xf0)) {
@@ -765,6 +806,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_R4700;
 		__cpu_name[cpu] = "R4700";
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS | MIPS_CPU_FPU | MIPS_CPU_32FPR |
 			     MIPS_CPU_LLSC;
 		c->tlbsize = 48;
@@ -773,6 +815,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_TX49XX;
 		__cpu_name[cpu] = "R49XX";
 		set_isa(c, MIPS_CPU_ISA_III);
+		c->fpu_msk31 |= FPU_CSR_CONDX;
 		c->options = R4K_OPTS | MIPS_CPU_LLSC;
 		if (!(c->processor_id & 0x08))
 			c->options |= MIPS_CPU_FPU | MIPS_CPU_32FPR;
@@ -814,6 +857,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_R6000;
 		__cpu_name[cpu] = "R6000";
 		set_isa(c, MIPS_CPU_ISA_II);
+		c->fpu_msk31 |= FPU_CSR_CONDX | FPU_CSR_FS;
 		c->options = MIPS_CPU_TLB | MIPS_CPU_FPU |
 			     MIPS_CPU_LLSC;
 		c->tlbsize = 32;
@@ -822,6 +866,7 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 		c->cputype = CPU_R6000A;
 		__cpu_name[cpu] = "R6000A";
 		set_isa(c, MIPS_CPU_ISA_II);
+		c->fpu_msk31 |= FPU_CSR_CONDX | FPU_CSR_FS;
 		c->options = MIPS_CPU_TLB | MIPS_CPU_FPU |
 			     MIPS_CPU_LLSC;
 		c->tlbsize = 32;
@@ -893,12 +938,14 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
 			__cpu_name[cpu] = "ICT Loongson-2";
 			set_elf_platform(cpu, "loongson2e");
 			set_isa(c, MIPS_CPU_ISA_III);
+			c->fpu_msk31 |= FPU_CSR_CONDX;
 			break;
 		case PRID_REV_LOONGSON2F:
 			c->cputype = CPU_LOONGSON2;
 			__cpu_name[cpu] = "ICT Loongson-2";
 			set_elf_platform(cpu, "loongson2f");
 			set_isa(c, MIPS_CPU_ISA_III);
+			c->fpu_msk31 |= FPU_CSR_CONDX;
 			break;
 		case PRID_REV_LOONGSON3A:
 			c->cputype = CPU_LOONGSON3;
@@ -1335,6 +1382,9 @@ void cpu_probe(void)
 	c->cputype	= CPU_UNKNOWN;
 	c->writecombine = _CACHE_UNCACHED;
 
+	c->fpu_csr31	= FPU_CSR_RN;
+	c->fpu_msk31	= FPU_CSR_RSVD | FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
+
 	c->processor_id = read_c0_prid();
 	switch (c->processor_id & PRID_COMP_MASK) {
 	case PRID_COMP_LEGACY:
@@ -1393,6 +1443,7 @@ void cpu_probe(void)
 
 	if (c->options & MIPS_CPU_FPU) {
 		c->fpu_id = cpu_get_fpu_id();
+		mips_nofpu_msk31 = c->fpu_msk31;
 
 		if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
 				    MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
@@ -1402,6 +1453,8 @@ void cpu_probe(void)
 			if (c->fpu_id & MIPS_FPIR_FREP)
 				c->options |= MIPS_CPU_FRE;
 		}
+
+		cpu_set_fpu_fcsr_mask(c);
 	} else
 		cpu_set_nofpu_id(c);
 
diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index 510452812594..6d1e3f8005f7 100644
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -32,6 +32,7 @@
 
 #include <asm/byteorder.h>
 #include <asm/cpu.h>
+#include <asm/cpu-info.h>
 #include <asm/dsp.h>
 #include <asm/fpu.h>
 #include <asm/mipsregs.h>
@@ -137,6 +138,9 @@ int ptrace_setfpregs(struct task_struct *child, __u32 __user *data)
 {
 	union fpureg *fregs;
 	u64 fpr_val;
+	u32 fcr31;
+	u32 value;
+	u32 mask;
 	int i;
 
 	if (!access_ok(VERIFY_READ, data, 33 * 8))
@@ -149,8 +153,10 @@ int ptrace_setfpregs(struct task_struct *child, __u32 __user *data)
 		set_fpr64(&fregs[i], 0, fpr_val);
 	}
 
-	__get_user(child->thread.fpu.fcr31, data + 64);
-	child->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
+	__get_user(value, data + 64);
+	fcr31 = child->thread.fpu.fcr31;
+	mask = current_cpu_data.fpu_msk31;
+	child->thread.fpu.fcr31 = (value & ~mask) | (fcr31 & mask);
 
 	/* FIR may not be written.  */
 
diff --git a/arch/mips/kernel/r2300_switch.S b/arch/mips/kernel/r2300_switch.S
index 435ea652f5fa..5087a4b72e6b 100644
--- a/arch/mips/kernel/r2300_switch.S
+++ b/arch/mips/kernel/r2300_switch.S
@@ -115,11 +115,9 @@ LEAF(_restore_fp)
  * the property that no matter whether considered as single or as double
  * precision represents signaling NANS.
  *
- * We initialize fcr31 to rounding to nearest, no exceptions.
+ * The value to initialize fcr31 to comes in $a0.
  */
 
-#define FPU_DEFAULT  0x00000000
-
 	.set push
 	SET_HARDFLOAT
 
@@ -129,8 +127,7 @@ LEAF(_init_fpu)
 	or	t0, t1
 	mtc0	t0, CP0_STATUS
 
-	li	t1, FPU_DEFAULT
-	ctc1	t1, fcr31
+	ctc1	a0, fcr31
 
 	li	t0, -1
 
diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S
index 3b1a36f13a7d..04cbbde3521b 100644
--- a/arch/mips/kernel/r4k_switch.S
+++ b/arch/mips/kernel/r4k_switch.S
@@ -165,11 +165,9 @@ LEAF(_init_msa_upper)
  * the property that no matter whether considered as single or as double
  * precision represents signaling NANS.
  *
- * We initialize fcr31 to rounding to nearest, no exceptions.
+ * The value to initialize fcr31 to comes in $a0.
  */
 
-#define FPU_DEFAULT  0x00000000
-
 	.set push
 	SET_HARDFLOAT
 
@@ -180,8 +178,7 @@ LEAF(_init_fpu)
 	mtc0	t0, CP0_STATUS
 	enable_fpu_hazard
 
-	li	t1, FPU_DEFAULT
-	ctc1	t1, fcr31
+	ctc1	a0, fcr31
 
 	li	t1, -1				# SNaN
 
diff --git a/arch/mips/loongson/loongson-3/cop2-ex.c b/arch/mips/loongson/loongson-3/cop2-ex.c
index b03e37d2071a..ea13764d0a03 100644
--- a/arch/mips/loongson/loongson-3/cop2-ex.c
+++ b/arch/mips/loongson/loongson-3/cop2-ex.c
@@ -43,7 +43,7 @@ static int loongson_cu2_call(struct notifier_block *nfb, unsigned long action,
 		if (!fpu_owned) {
 			set_thread_flag(TIF_USEDFPU);
 			if (!used_math()) {
-				_init_fpu();
+				_init_fpu(current->thread.fpu.fcr31);
 				set_used_math();
 			} else
 				_restore_fp(current);
diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index 3a90170a6277..d31c537ace1d 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -908,6 +908,7 @@ static inline void cop1_ctc(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
 {
 	u32 fcr31 = ctx->fcr31;
 	u32 value;
+	u32 mask;
 
 	if (MIPSInst_RT(ir) == 0)
 		value = 0;
@@ -919,9 +920,9 @@ static inline void cop1_ctc(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
 		pr_debug("%p gpr[%d]->csr=%08x\n",
 			 (void *)xcp->cp0_epc, MIPSInst_RT(ir), value);
 
-		/* Don't write unsupported bits.  */
-		fcr31 = value &
-			~(FPU_CSR_RSVD | FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
+		/* Preserve read-only bits.  */
+		mask = current_cpu_data.fpu_msk31;
+		fcr31 = (value & ~mask) | (fcr31 & mask);
 		break;
 
 	case FPCREG_FENR: