[PATCH 3.16 100/254] MIPS: Respect the ISA level in FCSR handling

From: Ben Hutchings
Date: Wed Feb 28 2018 - 11:03:39 EST

3.16.55-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: "Maciej W. Rozycki" <macro@xxxxxxxxxxxxxx>

commit 9b26616c8d9dae53fbac7f7cb2c6dd1308102976 upstream.

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@xxxxxxxxxxxxxx: Fixed double inclusion of <asm/current.h>.]

Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/9711/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
- In cop1Emulate(), keep converting the rounding mode
- Drop change in loongson_cu2_call()
- Add definitions of FPU_CSR_{FS,CONDX} in <asm/mipsregs.h>
- Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- 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;
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -9,6 +9,9 @@
#define _ASM_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. */
@@ -273,6 +276,8 @@ do { \
set_personality(PER_LINUX); \
\
current->thread.abi = &mips_abi; \
+ \
+ current->thread.fpu.fcr31 = current_cpu_data.fpu_csr31; \
} while (0)

#endif /* CONFIG_32BIT */
@@ -332,6 +337,8 @@ 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); \
--- 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 *);

@@ -163,6 +163,7 @@ static inline void lose_fpu(int save)

static inline int init_fpu(void)
{
+ unsigned int fcr31 = current->thread.fpu.fcr31;
int ret = 0;

preempt_disable();
@@ -170,7 +171,7 @@ static inline int init_fpu(void)
if (cpu_has_fpu) {
ret = __own_fpu();
if (!ret)
- _init_fpu();
+ _init_fpu(fcr31);
} else
fpu_emulator_init_fpu();

--- a/arch/mips/include/asm/fpu_emulator.h
+++ b/arch/mips/include/asm/fpu_emulator.h
@@ -87,8 +87,6 @@ static inline void fpu_emulator_init_fpu
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);
}
--- a/arch/mips/kernel/cpu-probe.c
+++ b/arch/mips/kernel/cpu-probe.c
@@ -30,11 +30,44 @@
#include <asm/spram.h>
#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;
+}
+
+/* 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)
{
- cpu_data[0].options &= ~MIPS_CPU_FPU;
+ boot_cpu_data.options &= ~MIPS_CPU_FPU;
+ boot_cpu_data.fpu_msk31 = mips_nofpu_msk31;
mips_fpu_disabled = 1;

return 1;
@@ -470,6 +503,7 @@ static inline void cpu_probe_legacy(stru
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())
@@ -489,6 +523,7 @@ static inline void cpu_probe_legacy(stru
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())
@@ -537,6 +572,7 @@ static inline void cpu_probe_legacy(stru
}

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;
@@ -544,6 +580,7 @@ static inline void cpu_probe_legacy(stru
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) {
@@ -585,6 +622,7 @@ static inline void cpu_probe_legacy(stru
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;
@@ -593,6 +631,7 @@ static inline void cpu_probe_legacy(stru
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;
@@ -608,11 +647,13 @@ static inline void cpu_probe_legacy(stru
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)) {
@@ -638,6 +679,7 @@ static inline void cpu_probe_legacy(stru
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;
@@ -646,6 +688,7 @@ static inline void cpu_probe_legacy(stru
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;
@@ -687,6 +730,7 @@ static inline void cpu_probe_legacy(stru
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;
@@ -695,6 +739,7 @@ static inline void cpu_probe_legacy(stru
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;
@@ -760,11 +805,13 @@ static inline void cpu_probe_legacy(stru
c->cputype = CPU_LOONGSON2;
__cpu_name[cpu] = "ICT Loongson-2";
set_elf_platform(cpu, "loongson2e");
+ 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");
+ c->fpu_msk31 |= FPU_CSR_CONDX;
break;
case PRID_REV_LOONGSON3A:
c->cputype = CPU_LOONGSON3;
@@ -1168,6 +1215,9 @@ void cpu_probe(void)
c->fpu_id = FPIR_IMP_NONE;
c->cputype = CPU_UNKNOWN;

+ 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:
@@ -1220,12 +1270,15 @@ 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_M32R2 |
MIPS_CPU_ISA_M64R1 | MIPS_CPU_ISA_M64R2)) {
if (c->fpu_id & MIPS_FPIR_3D)
c->ases |= MIPS_ASE_MIPS3D;
}
+
+ cpu_set_fpu_fcsr_mask(c);
}

if (cpu_has_mips_r2) {
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -33,6 +33,7 @@

#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>
@@ -158,6 +159,9 @@ int ptrace_setfpregs(struct task_struct
{
union fpureg *fregs;
u64 fpr_val;
+ u32 fcr31;
+ u32 value;
+ u32 mask;
int i;

if (!access_ok(VERIFY_READ, data, 33 * 8))
@@ -171,8 +175,10 @@ int ptrace_setfpregs(struct task_struct
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. */

--- 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

--- a/arch/mips/kernel/r4k_switch.S
+++ b/arch/mips/kernel/r4k_switch.S
@@ -163,11 +163,9 @@ 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

@@ -178,8 +176,7 @@ LEAF(_init_fpu)
mtc0 t0, CP0_STATUS
enable_fpu_hazard

- li t1, FPU_DEFAULT
- ctc1 t1, fcr31
+ ctc1 a0, fcr31

li t1, -1 # SNaN

--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -924,17 +924,19 @@ emul:
/* we only have one writable control reg
*/
if (MIPSInst_RD(ir) == FPCREG_CSR) {
+ u32 mask;
+
pr_debug("%p gpr[%d]->csr=%08x\n",
(void *) (xcp->cp0_epc),
MIPSInst_RT(ir), value);

/*
- * Don't write unsupported bits,
+ * Preserve read-only bits,
* and convert to ieee library modes
*/
- ctx->fcr31 = (value &
- ~(FPU_CSR_RSVD | FPU_CSR_ABS2008 |
- FPU_CSR_NAN2008 | FPU_CSR_RM)) |
+ mask = current_cpu_data.fpu_msk31;
+ ctx->fcr31 = (value & ~(mask | FPU_CSR_RM)) |
+ (ctx->fcr31 & mask) |
modeindex(value);
}
if ((ctx->fcr31 >> 5) & ctx->fcr31 & FPU_CSR_ALL_E) {
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -123,6 +123,11 @@
/*
* Status Register Values
*/
+#define FPU_CSR_FS_S 24 /* flush denormalised results to 0 */
+#define FPU_CSR_FS (_ULCAST_(1) << FPU_CSR_FS_S)
+
+#define FPU_CSR_CONDX_S 25 /* $fcc[7:1] */
+#define FPU_CSR_CONDX (_ULCAST_(127) << FPU_CSR_CONDX_S)

#define FPU_CSR_FLUSH 0x01000000 /* flush denormalised results to 0 */
#define FPU_CSR_COND 0x00800000 /* $fcc0 */