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MIPS: Simplify FP context initialization

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MIPS has up until now had 3 different ways for a task's floating point
context to be initialized:

  - If the task's first use of FP involves it gaining ownership of an
    FPU then _init_fpu() is used to initialize the FPU's registers such
    that they all contain ~0, and the FPU registers will be stored to
    struct thread_info later (eg. when context switching).

  - If the task first uses FP on a CPU without an associated FPU then
    fpu_emulator_init_fpu() initializes the task's floating point
    register state in struct thread_info such that all floating point
    register contain the bit pattern 0x7ff800007ff80000, different to
    the _init_fpu() behaviour.

  - If a task's floating point context is first accessed via ptrace then
    init_fp_ctx() initializes the floating point register state in
    struct thread_info to ~0, giving equivalent state to _init_fpu().

The _init_fpu() path has 2 separate implementations - one for r2k/r3k
style systems & one for r4k style systems. The _init_fpu() path also
requires that we be careful to clear & restore the value of the
Config5.FRE bit on modern systems in order to avoid inadvertently
triggering floating point exceptions.

None of this code is in a performance critical hot path - it runs only
the first time a task uses floating point. As such it doesn't seem to
warrant the complications of maintaining the _init_fpu() path.

Remove _init_fpu() & fpu_emulator_init_fpu(), instead using
init_fp_ctx() consistently to initialize floating point register state
in struct thread_info. Upon a task's first use of floating point this
will typically mean that we initialize state in memory & then load it
into FPU registers using _restore_fp() just as we would on a context
switch. For other paths such as __compute_return_epc_for_insn() or
mipsr2_decoder() this results in a significant simplification of the
work to be done.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21002/
Cc: linux-mips@linux-mips.org
This commit is contained in:
Paul Burton 2018-11-07 23:13:59 +00:00
parent b1013f1e95
commit cc97ab235f
No known key found for this signature in database
GPG Key ID: 3EA79FACB57500DD
9 changed files with 38 additions and 292 deletions
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57
arch/mips/include/asm/fpu.h
View File

@ -33,7 +33,6 @@
struct sigcontext;
struct sigcontext32;
extern void _init_fpu(unsigned int);
extern void _save_fp(struct task_struct *);
extern void _restore_fp(struct task_struct *);
@ -198,42 +197,36 @@ static inline void lose_fpu(int save)
preempt_enable();
}
static inline int init_fpu(void)
/**
* init_fp_ctx() - Initialize task FP context
* @target: The task whose FP context should be initialized.
*
* Initializes the FP context of the target task to sane default values if that
* target task does not already have valid FP context. Once the context has
* been initialized, the task will be marked as having used FP & thus having
* valid FP context.
*
* Returns: true if context is initialized, else false.
*/
static inline bool init_fp_ctx(struct task_struct *target)
{
unsigned int fcr31 = current->thread.fpu.fcr31;
int ret = 0;
/* If FP has been used then the target already has context */
if (tsk_used_math(target))
return false;
if (cpu_has_fpu) {
unsigned int config5;
/* Begin with data registers set to all 1s... */
memset(&target->thread.fpu.fpr, ~0, sizeof(target->thread.fpu.fpr));
ret = __own_fpu();
if (ret)
return ret;
/* FCSR has been preset by `mips_set_personality_nan'. */
if (!cpu_has_fre) {
_init_fpu(fcr31);
/*
* Record that the target has "used" math, such that the context
* just initialised, and any modifications made by the caller,
* aren't discarded.
*/
set_stopped_child_used_math(target);
return 0;
}
/*
* Ensure FRE is clear whilst running _init_fpu, since
* single precision FP instructions are used. If FRE
* was set then we'll just end up initialising all 32
* 64b registers.
*/
config5 = clear_c0_config5(MIPS_CONF5_FRE);
enable_fpu_hazard();
_init_fpu(fcr31);
/* Restore FRE */
write_c0_config5(config5);
enable_fpu_hazard();
} else
fpu_emulator_init_fpu();
return ret;
return true;
}
static inline void save_fp(struct task_struct *tsk)

11
arch/mips/include/asm/fpu_emulator.h
View File

@ -188,17 +188,6 @@ int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
unsigned long *contpc);
#define SIGNALLING_NAN 0x7ff800007ff80000LL
static inline void fpu_emulator_init_fpu(void)
{
struct task_struct *t = current;
int i;
for (i = 0; i < 32; i++)
set_fpr64(&t->thread.fpu.fpr[i], 0, SIGNALLING_NAN);
}
/*
* Mask the FCSR Cause bits according to the Enable bits, observing
* that Unimplemented is always enabled.

12
arch/mips/kernel/branch.c
View File

@ -674,16 +674,8 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
if (cpu_has_mips_r6 &&
((insn.i_format.rs == bc1eqz_op) ||
(insn.i_format.rs == bc1nez_op))) {
if (!used_math()) { /* First time FPU user */
ret = init_fpu();
if (ret && NO_R6EMU) {
ret = -ret;
break;
}
ret = 0;
set_used_math();
}
lose_fpu(1); /* Save FPU state for the emulator. */
if (!init_fp_ctx(current))
lose_fpu(1);
reg = insn.i_format.rt;
bit = get_fpr32(&current->thread.fpu.fpr[reg], 0) & 0x1;
if (insn.i_format.rs == bc1eqz_op)

10
arch/mips/kernel/mips-r2-to-r6-emul.c
View File

@ -1174,13 +1174,9 @@ int mipsr2_decoder(struct pt_regs *regs, u32 inst, unsigned long *fcr31)
fpu_emul:
regs->regs[31] = r31;
regs->cp0_epc = epc;
if (!used_math()) { /* First time FPU user. */
preempt_disable();
err = init_fpu();
preempt_enable();
set_used_math();
}
lose_fpu(1); /* Save FPU state for the emulator. */
if (!init_fp_ctx(current))
lose_fpu(1);
err = fpu_emulator_cop1Handler(regs, &current->thread.fpu, 0,
&fault_addr);

19
arch/mips/kernel/ptrace.c
View File

@ -50,25 +50,6 @@
#define CREATE_TRACE_POINTS
#include <trace/events/syscalls.h>
static void init_fp_ctx(struct task_struct *target)
{
/* If FP has been used then the target already has context */
if (tsk_used_math(target))
return;
/* Begin with data registers set to all 1s... */
memset(&target->thread.fpu.fpr, ~0, sizeof(target->thread.fpu.fpr));
/* FCSR has been preset by `mips_set_personality_nan'. */
/*
* Record that the target has "used" math, such that the context
* just initialised, and any modifications made by the caller,
* aren't discarded.
*/
set_stopped_child_used_math(target);
}
/*
* Called by kernel/ptrace.c when detaching..
*

58
arch/mips/kernel/r2300_fpu.S
View File

@ -52,64 +52,6 @@ LEAF(_restore_fp)
jr ra
END(_restore_fp)
/*
* Load the FPU with signalling NANS. This bit pattern we're using has
* the property that no matter whether considered as single or as double
* precision represents signaling NANS.
*
* The value to initialize fcr31 to comes in $a0.
*/
.set push
SET_HARDFLOAT
LEAF(_init_fpu)
mfc0 t0, CP0_STATUS
li t1, ST0_CU1
or t0, t1
mtc0 t0, CP0_STATUS
ctc1 a0, fcr31
li t0, -1
mtc1 t0, $f0
mtc1 t0, $f1
mtc1 t0, $f2
mtc1 t0, $f3
mtc1 t0, $f4
mtc1 t0, $f5
mtc1 t0, $f6
mtc1 t0, $f7
mtc1 t0, $f8
mtc1 t0, $f9
mtc1 t0, $f10
mtc1 t0, $f11
mtc1 t0, $f12
mtc1 t0, $f13
mtc1 t0, $f14
mtc1 t0, $f15
mtc1 t0, $f16
mtc1 t0, $f17
mtc1 t0, $f18
mtc1 t0, $f19
mtc1 t0, $f20
mtc1 t0, $f21
mtc1 t0, $f22
mtc1 t0, $f23
mtc1 t0, $f24
mtc1 t0, $f25
mtc1 t0, $f26
mtc1 t0, $f27
mtc1 t0, $f28
mtc1 t0, $f29
mtc1 t0, $f30
mtc1 t0, $f31
jr ra
END(_init_fpu)
.set pop
.set noreorder
/**

144
arch/mips/kernel/r4k_fpu.S
View File

@ -86,150 +86,6 @@ LEAF(_init_msa_upper)
#endif
/*
* Load the FPU with signalling NANS. This bit pattern we're using has
* the property that no matter whether considered as single or as double
* precision represents signaling NANS.
*
* The value to initialize fcr31 to comes in $a0.
*/
.set push
SET_HARDFLOAT
LEAF(_init_fpu)
mfc0 t0, CP0_STATUS
li t1, ST0_CU1
or t0, t1
mtc0 t0, CP0_STATUS
enable_fpu_hazard
ctc1 a0, fcr31
li t1, -1 # SNaN
#ifdef CONFIG_64BIT
sll t0, t0, 5
bgez t0, 1f # 16 / 32 register mode?
dmtc1 t1, $f1
dmtc1 t1, $f3
dmtc1 t1, $f5
dmtc1 t1, $f7
dmtc1 t1, $f9
dmtc1 t1, $f11
dmtc1 t1, $f13
dmtc1 t1, $f15
dmtc1 t1, $f17
dmtc1 t1, $f19
dmtc1 t1, $f21
dmtc1 t1, $f23
dmtc1 t1, $f25
dmtc1 t1, $f27
dmtc1 t1, $f29
dmtc1 t1, $f31
1:
#endif
#ifdef CONFIG_CPU_MIPS32
mtc1 t1, $f0
mtc1 t1, $f1
mtc1 t1, $f2
mtc1 t1, $f3
mtc1 t1, $f4
mtc1 t1, $f5
mtc1 t1, $f6
mtc1 t1, $f7
mtc1 t1, $f8
mtc1 t1, $f9
mtc1 t1, $f10
mtc1 t1, $f11
mtc1 t1, $f12
mtc1 t1, $f13
mtc1 t1, $f14
mtc1 t1, $f15
mtc1 t1, $f16
mtc1 t1, $f17
mtc1 t1, $f18
mtc1 t1, $f19
mtc1 t1, $f20
mtc1 t1, $f21
mtc1 t1, $f22
mtc1 t1, $f23
mtc1 t1, $f24
mtc1 t1, $f25
mtc1 t1, $f26
mtc1 t1, $f27
mtc1 t1, $f28
mtc1 t1, $f29
mtc1 t1, $f30
mtc1 t1, $f31
#if defined(CONFIG_CPU_MIPS32_R2) || defined(CONFIG_CPU_MIPS32_R6)
.set push
.set MIPS_ISA_LEVEL_RAW
.set fp=64
sll t0, t0, 5 # is Status.FR set?
bgez t0, 1f # no: skip setting upper 32b
mthc1 t1, $f0
mthc1 t1, $f1
mthc1 t1, $f2
mthc1 t1, $f3
mthc1 t1, $f4
mthc1 t1, $f5
mthc1 t1, $f6
mthc1 t1, $f7
mthc1 t1, $f8
mthc1 t1, $f9
mthc1 t1, $f10
mthc1 t1, $f11
mthc1 t1, $f12
mthc1 t1, $f13
mthc1 t1, $f14
mthc1 t1, $f15
mthc1 t1, $f16
mthc1 t1, $f17
mthc1 t1, $f18
mthc1 t1, $f19
mthc1 t1, $f20
mthc1 t1, $f21
mthc1 t1, $f22
mthc1 t1, $f23
mthc1 t1, $f24
mthc1 t1, $f25
mthc1 t1, $f26
mthc1 t1, $f27
mthc1 t1, $f28
mthc1 t1, $f29
mthc1 t1, $f30
mthc1 t1, $f31
1: .set pop
#endif /* CONFIG_CPU_MIPS32_R2 || CONFIG_CPU_MIPS32_R6 */
#else
.set MIPS_ISA_ARCH_LEVEL_RAW
dmtc1 t1, $f0
dmtc1 t1, $f2
dmtc1 t1, $f4
dmtc1 t1, $f6
dmtc1 t1, $f8
dmtc1 t1, $f10
dmtc1 t1, $f12
dmtc1 t1, $f14
dmtc1 t1, $f16
dmtc1 t1, $f18
dmtc1 t1, $f20
dmtc1 t1, $f22
dmtc1 t1, $f24
dmtc1 t1, $f26
dmtc1 t1, $f28
dmtc1 t1, $f30
#endif
jr ra
END(_init_fpu)
.set pop /* SET_HARDFLOAT */
.set noreorder
/**

12
arch/mips/kernel/traps.c
View File

@ -1218,20 +1218,20 @@ static int default_cu2_call(struct notifier_block *nfb, unsigned long action,
static int enable_restore_fp_context(int msa)
{
int err, was_fpu_owner, prior_msa;
bool first_fp;
if (!used_math()) {
/* First time FP context user. */
/* Initialize context if it hasn't been used already */
first_fp = init_fp_ctx(current);
if (first_fp) {
preempt_disable();
err = init_fpu();
err = own_fpu_inatomic(1);
if (msa && !err) {
enable_msa();
init_msa_upper();
set_thread_flag(TIF_USEDMSA);
set_thread_flag(TIF_MSA_CTX_LIVE);
}
preempt_enable();
if (!err)
set_used_math();
return err;
}

7
arch/mips/loongson64/loongson-3/cop2-ex.c
View File

@ -43,11 +43,8 @@ static int loongson_cu2_call(struct notifier_block *nfb, unsigned long action,
/* If FPU is owned, we needn't init or restore fp */
if (!fpu_owned) {
set_thread_flag(TIF_USEDFPU);
if (!used_math()) {
_init_fpu(current->thread.fpu.fcr31);
set_used_math();
} else
_restore_fp(current);
init_fp_ctx(current);
_restore_fp(current);
}
preempt_enable();