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MIPS: Basic MSA context switching support

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This patch adds support for context switching the MSA vector registers.
These 128 bit vector registers are aliased with the FP registers - an
FP register accesses the least significant bits of the vector register
with which it is aliased (ie. the register with the same index). Due to
both this & the requirement that the scalar FPU must be 64-bit (FR=1) if
enabled at the same time as MSA the kernel will enable MSA & scalar FP
at the same time for tasks which use MSA. If we restore the MSA vector
context then we might as well enable the scalar FPU since the reason it
was left disabled was to allow for lazy FP context restoring - but we
just restored the FP context as it's a subset of the vector context. If
we restore the FP context and have previously used MSA then we have to
restore the whole vector context anyway (see comment in
enable_restore_fp_context for details) so similarly we might as well
enable MSA.

Thus if a task does not use MSA then it will continue to behave as
without this patch - the scalar FP context will be saved & restored as
usual. But if a task executes an MSA instruction then it will save &
restore the vector context forever more.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6431/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton 2014-01-27 15:23:11 +00:00 committed by Ralf Baechle
parent a5e9a69e2c
commit 1db1af84d6
10 changed files with 275 additions and 34 deletions
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9
arch/mips/Kconfig
View File

@ -2090,10 +2090,11 @@ config CPU_HAS_MSA
help
MIPS SIMD Architecture (MSA) introduces 128 bit wide vector registers
and a set of SIMD instructions to operate on them. When this option
is enabled the kernel will support detection of the MSA ASE. If you
know that your kernel will only be running on CPUs which do not
support MSA then you may wish to say N here to reduce the size of
your kernel.
is enabled the kernel will support allocating & switching MSA
vector register contexts. If you know that your kernel will only be
running on CPUs which do not support MSA or that your userland will
not be making use of it then you may wish to say N here to reduce
the size & complexity of your kernel.
If unsure, say Y.

70
arch/mips/include/asm/asmmacro.h
View File

@ -328,4 +328,74 @@
.endm
#endif
.macro msa_save_all thread
st_d 0, THREAD_FPR0, \thread
st_d 1, THREAD_FPR1, \thread
st_d 2, THREAD_FPR2, \thread
st_d 3, THREAD_FPR3, \thread
st_d 4, THREAD_FPR4, \thread
st_d 5, THREAD_FPR5, \thread
st_d 6, THREAD_FPR6, \thread
st_d 7, THREAD_FPR7, \thread
st_d 8, THREAD_FPR8, \thread
st_d 9, THREAD_FPR9, \thread
st_d 10, THREAD_FPR10, \thread
st_d 11, THREAD_FPR11, \thread
st_d 12, THREAD_FPR12, \thread
st_d 13, THREAD_FPR13, \thread
st_d 14, THREAD_FPR14, \thread
st_d 15, THREAD_FPR15, \thread
st_d 16, THREAD_FPR16, \thread
st_d 17, THREAD_FPR17, \thread
st_d 18, THREAD_FPR18, \thread
st_d 19, THREAD_FPR19, \thread
st_d 20, THREAD_FPR20, \thread
st_d 21, THREAD_FPR21, \thread
st_d 22, THREAD_FPR22, \thread
st_d 23, THREAD_FPR23, \thread
st_d 24, THREAD_FPR24, \thread
st_d 25, THREAD_FPR25, \thread
st_d 26, THREAD_FPR26, \thread
st_d 27, THREAD_FPR27, \thread
st_d 28, THREAD_FPR28, \thread
st_d 29, THREAD_FPR29, \thread
st_d 30, THREAD_FPR30, \thread
st_d 31, THREAD_FPR31, \thread
.endm
.macro msa_restore_all thread
ld_d 0, THREAD_FPR0, \thread
ld_d 1, THREAD_FPR1, \thread
ld_d 2, THREAD_FPR2, \thread
ld_d 3, THREAD_FPR3, \thread
ld_d 4, THREAD_FPR4, \thread
ld_d 5, THREAD_FPR5, \thread
ld_d 6, THREAD_FPR6, \thread
ld_d 7, THREAD_FPR7, \thread
ld_d 8, THREAD_FPR8, \thread
ld_d 9, THREAD_FPR9, \thread
ld_d 10, THREAD_FPR10, \thread
ld_d 11, THREAD_FPR11, \thread
ld_d 12, THREAD_FPR12, \thread
ld_d 13, THREAD_FPR13, \thread
ld_d 14, THREAD_FPR14, \thread
ld_d 15, THREAD_FPR15, \thread
ld_d 16, THREAD_FPR16, \thread
ld_d 17, THREAD_FPR17, \thread
ld_d 18, THREAD_FPR18, \thread
ld_d 19, THREAD_FPR19, \thread
ld_d 20, THREAD_FPR20, \thread
ld_d 21, THREAD_FPR21, \thread
ld_d 22, THREAD_FPR22, \thread
ld_d 23, THREAD_FPR23, \thread
ld_d 24, THREAD_FPR24, \thread
ld_d 25, THREAD_FPR25, \thread
ld_d 26, THREAD_FPR26, \thread
ld_d 27, THREAD_FPR27, \thread
ld_d 28, THREAD_FPR28, \thread
ld_d 29, THREAD_FPR29, \thread
ld_d 30, THREAD_FPR30, \thread
ld_d 31, THREAD_FPR31, \thread
.endm
#endif /* _ASM_ASMMACRO_H */

28
arch/mips/include/asm/msa.h
View File

@ -12,6 +12,9 @@
#include <asm/mipsregs.h>
extern void _save_msa(struct task_struct *);
extern void _restore_msa(struct task_struct *);
static inline void enable_msa(void)
{
if (cpu_has_msa) {
@ -36,6 +39,31 @@ static inline int is_msa_enabled(void)
return read_c0_config5() & MIPS_CONF5_MSAEN;
}
static inline int thread_msa_context_live(void)
{
/*
* Check cpu_has_msa only if it's a constant. This will allow the
* compiler to optimise out code for CPUs without MSA without adding
* an extra redundant check for CPUs with MSA.
*/
if (__builtin_constant_p(cpu_has_msa) && !cpu_has_msa)
return 0;
return test_thread_flag(TIF_MSA_CTX_LIVE);
}
static inline void save_msa(struct task_struct *t)
{
if (cpu_has_msa)
_save_msa(t);
}
static inline void restore_msa(struct task_struct *t)
{
if (cpu_has_msa)
_restore_msa(t);
}
#ifdef TOOLCHAIN_SUPPORTS_MSA
#define __BUILD_MSA_CTL_REG(name, cs) \

9
arch/mips/include/asm/processor.h
View File

@ -96,7 +96,12 @@ extern unsigned int vced_count, vcei_count;
#define NUM_FPU_REGS 32
#define FPU_REG_WIDTH 64
#ifdef CONFIG_CPU_HAS_MSA
# define FPU_REG_WIDTH 128
#else
# define FPU_REG_WIDTH 64
#endif
union fpureg {
__u32 val32[FPU_REG_WIDTH / 32];
@ -133,6 +138,7 @@ BUILD_FPR_ACCESS(64)
struct mips_fpu_struct {
union fpureg fpr[NUM_FPU_REGS];
unsigned int fcr31;
unsigned int msacsr;
};
#define NUM_DSP_REGS 6
@ -310,6 +316,7 @@ struct thread_struct {
.fpu = { \
.fpr = {{{0,},},}, \
.fcr31 = 0, \
.msacsr = 0, \
}, \
/* \
* FPU affinity state (null if not FPAFF) \

22
arch/mips/include/asm/switch_to.h
View File

@ -16,22 +16,29 @@
#include <asm/watch.h>
#include <asm/dsp.h>
#include <asm/cop2.h>
#include <asm/msa.h>
struct task_struct;
enum {
FP_SAVE_NONE = 0,
FP_SAVE_VECTOR = -1,
FP_SAVE_SCALAR = 1,
};
/**
* resume - resume execution of a task
* @prev: The task previously executed.
* @next: The task to begin executing.
* @next_ti: task_thread_info(next).
* @usedfpu: Non-zero if prev's FP context should be saved.
* @fp_save: Which, if any, FP context to save for prev.
*
* This function is used whilst scheduling to save the context of prev & load
* the context of next. Returns prev.
*/
extern asmlinkage struct task_struct *resume(struct task_struct *prev,
struct task_struct *next, struct thread_info *next_ti,
u32 usedfpu);
s32 fp_save);
extern unsigned int ll_bit;
extern struct task_struct *ll_task;
@ -75,7 +82,8 @@ do { \
#define switch_to(prev, next, last) \
do { \
u32 __usedfpu, __c0_stat; \
u32 __c0_stat; \
s32 __fpsave = FP_SAVE_NONE; \
__mips_mt_fpaff_switch_to(prev); \
if (cpu_has_dsp) \
__save_dsp(prev); \
@ -88,8 +96,12 @@ do { \
write_c0_status(__c0_stat & ~ST0_CU2); \
} \
__clear_software_ll_bit(); \
__usedfpu = test_and_clear_tsk_thread_flag(prev, TIF_USEDFPU); \
(last) = resume(prev, next, task_thread_info(next), __usedfpu); \
if (test_and_clear_tsk_thread_flag(prev, TIF_USEDFPU)) \
__fpsave = FP_SAVE_SCALAR; \
if (test_and_clear_tsk_thread_flag(prev, TIF_USEDMSA)) \
__fpsave = FP_SAVE_VECTOR; \
(last) = resume(prev, next, task_thread_info(next), __fpsave); \
disable_msa(); \
} while (0)
#define finish_arch_switch(prev) \

4
arch/mips/include/asm/thread_info.h
View File

@ -116,6 +116,8 @@ static inline struct thread_info *current_thread_info(void)
#define TIF_LOAD_WATCH 25 /* If set, load watch registers */
#define TIF_SYSCALL_TRACEPOINT 26 /* syscall tracepoint instrumentation */
#define TIF_32BIT_FPREGS 27 /* 32-bit floating point registers */
#define TIF_USEDMSA 29 /* MSA has been used this quantum */
#define TIF_MSA_CTX_LIVE 30 /* MSA context must be preserved */
#define TIF_SYSCALL_TRACE 31 /* syscall trace active */
#define _TIF_SYSCALL_TRACE (1<<TIF_SYSCALL_TRACE)
@ -133,6 +135,8 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_FPUBOUND (1<<TIF_FPUBOUND)
#define _TIF_LOAD_WATCH (1<<TIF_LOAD_WATCH)
#define _TIF_32BIT_FPREGS (1<<TIF_32BIT_FPREGS)
#define _TIF_USEDMSA (1<<TIF_USEDMSA)
#define _TIF_MSA_CTX_LIVE (1<<TIF_MSA_CTX_LIVE)
#define _TIF_SYSCALL_TRACEPOINT (1<<TIF_SYSCALL_TRACEPOINT)
#define _TIF_WORK_SYSCALL_ENTRY (_TIF_NOHZ | _TIF_SYSCALL_TRACE | \

1
arch/mips/kernel/genex.S
View File

@ -477,6 +477,7 @@ NESTED(nmi_handler, PT_SIZE, sp)
BUILD_HANDLER tr tr sti silent /* #13 */
BUILD_HANDLER fpe fpe fpe silent /* #15 */
BUILD_HANDLER ftlb ftlb none silent /* #16 */
BUILD_HANDLER msa msa sti silent /* #21 */
BUILD_HANDLER mdmx mdmx sti silent /* #22 */
#ifdef CONFIG_HARDWARE_WATCHPOINTS
/*

7
arch/mips/kernel/process.c
View File

@ -32,6 +32,7 @@
#include <asm/cpu.h>
#include <asm/dsp.h>
#include <asm/fpu.h>
#include <asm/msa.h>
#include <asm/pgtable.h>
#include <asm/mipsregs.h>
#include <asm/processor.h>
@ -65,6 +66,8 @@ void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long sp)
clear_used_math();
clear_fpu_owner();
init_dsp();
clear_thread_flag(TIF_MSA_CTX_LIVE);
disable_msa();
regs->cp0_epc = pc;
regs->regs[29] = sp;
}
@ -89,7 +92,9 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
preempt_disable();
if (is_fpu_owner())
if (is_msa_enabled())
save_msa(p);
else if (is_fpu_owner())
save_fp(p);
if (cpu_has_dsp)

58
arch/mips/kernel/r4k_switch.S
View File

@ -28,19 +28,9 @@
*/
#define ST_OFF (_THREAD_SIZE - 32 - PT_SIZE + PT_STATUS)
/*
* FPU context is saved iff the process has used it's FPU in the current
* time slice as indicated by _TIF_USEDFPU. In any case, the CU1 bit for user
* space STATUS register should be 0, so that a process *always* starts its
* userland with FPU disabled after each context switch.
*
* FPU will be enabled as soon as the process accesses FPU again, through
* do_cpu() trap.
*/
/*
* task_struct *resume(task_struct *prev, task_struct *next,
* struct thread_info *next_ti, int usedfpu)
* struct thread_info *next_ti, s32 fp_save)
*/
.align 5
LEAF(resume)
@ -50,23 +40,37 @@
LONG_S ra, THREAD_REG31(a0)
/*
* check if we need to save FPU registers
* Check whether we need to save any FP context. FP context is saved
* iff the process has used the context with the scalar FPU or the MSA
* ASE in the current time slice, as indicated by _TIF_USEDFPU and
* _TIF_USEDMSA respectively. switch_to will have set fp_save
* accordingly to an FP_SAVE_ enum value.
*/
beqz a3, 2f
beqz a3, 1f
PTR_L t3, TASK_THREAD_INFO(a0)
/*
* clear saved user stack CU1 bit
* We do. Clear the saved CU1 bit for prev, such that next time it is
* scheduled it will start in userland with the FPU disabled. If the
* task uses the FPU then it will be enabled again via the do_cpu trap.
* This allows us to lazily restore the FP context.
*/
PTR_L t3, TASK_THREAD_INFO(a0)
LONG_L t0, ST_OFF(t3)
li t1, ~ST0_CU1
and t0, t0, t1
LONG_S t0, ST_OFF(t3)
/* Check whether we're saving scalar or vector context. */
bgtz a3, 1f
/* Save 128b MSA vector context. */
msa_save_all a0
b 2f
1: /* Save 32b/64b scalar FP context. */
fpu_save_double a0 t0 t1 # c0_status passed in t0
# clobbers t1
1:
2:
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
PTR_LA t8, __stack_chk_guard
@ -141,6 +145,26 @@ LEAF(_restore_fp)
jr ra
END(_restore_fp)
#ifdef CONFIG_CPU_HAS_MSA
/*
* Save a thread's MSA vector context.
*/
LEAF(_save_msa)
msa_save_all a0
jr ra
END(_save_msa)
/*
* Restore a thread's MSA vector context.
*/
LEAF(_restore_msa)
msa_restore_all a0
jr ra
END(_restore_msa)
#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

101
arch/mips/kernel/traps.c
View File

@ -47,6 +47,7 @@
#include <asm/mipsregs.h>
#include <asm/mipsmtregs.h>
#include <asm/module.h>
#include <asm/msa.h>
#include <asm/pgtable.h>
#include <asm/ptrace.h>
#include <asm/sections.h>
@ -79,6 +80,7 @@ extern asmlinkage void handle_ov(void);
extern asmlinkage void handle_tr(void);
extern asmlinkage void handle_fpe(void);
extern asmlinkage void handle_ftlb(void);
extern asmlinkage void handle_msa(void);
extern asmlinkage void handle_mdmx(void);
extern asmlinkage void handle_watch(void);
extern asmlinkage void handle_mt(void);
@ -1074,6 +1076,76 @@ static int default_cu2_call(struct notifier_block *nfb, unsigned long action,
return NOTIFY_OK;
}
static int enable_restore_fp_context(int msa)
{
int err, was_fpu_owner;
if (!used_math()) {
/* First time FP context user. */
err = init_fpu();
if (msa && !err)
enable_msa();
if (!err)
set_used_math();
return err;
}
/*
* This task has formerly used the FP context.
*
* If this thread has no live MSA vector context then we can simply
* restore the scalar FP context. If it has live MSA vector context
* (that is, it has or may have used MSA since last performing a
* function call) then we'll need to restore the vector context. This
* applies even if we're currently only executing a scalar FP
* instruction. This is because if we were to later execute an MSA
* instruction then we'd either have to:
*
* - Restore the vector context & clobber any registers modified by
* scalar FP instructions between now & then.
*
* or
*
* - Not restore the vector context & lose the most significant bits
* of all vector registers.
*
* Neither of those options is acceptable. We cannot restore the least
* significant bits of the registers now & only restore the most
* significant bits later because the most significant bits of any
* vector registers whose aliased FP register is modified now will have
* been zeroed. We'd have no way to know that when restoring the vector
* context & thus may load an outdated value for the most significant
* bits of a vector register.
*/
if (!msa && !thread_msa_context_live())
return own_fpu(1);
/*
* This task is using or has previously used MSA. Thus we require
* that Status.FR == 1.
*/
was_fpu_owner = is_fpu_owner();
err = own_fpu(0);
if (err)
return err;
enable_msa();
write_msa_csr(current->thread.fpu.msacsr);
set_thread_flag(TIF_USEDMSA);
/*
* If this is the first time that the task is using MSA and it has
* previously used scalar FP in this time slice then we already nave
* FP context which we shouldn't clobber.
*/
if (!test_and_set_thread_flag(TIF_MSA_CTX_LIVE) && was_fpu_owner)
return 0;
/* We need to restore the vector context. */
restore_msa(current);
return 0;
}
asmlinkage void do_cpu(struct pt_regs *regs)
{
enum ctx_state prev_state;
@ -1153,12 +1225,7 @@ asmlinkage void do_cpu(struct pt_regs *regs)
/* Fall through. */
case 1:
if (used_math()) /* Using the FPU again. */
err = own_fpu(1);
else { /* First time FPU user. */
err = init_fpu();
set_used_math();
}
err = enable_restore_fp_context(0);
if (!raw_cpu_has_fpu || err) {
int sig;
@ -1183,6 +1250,27 @@ out:
exception_exit(prev_state);
}
asmlinkage void do_msa(struct pt_regs *regs)
{
enum ctx_state prev_state;
int err;
prev_state = exception_enter();
if (!cpu_has_msa || test_thread_flag(TIF_32BIT_FPREGS)) {
force_sig(SIGILL, current);
goto out;
}
die_if_kernel("do_msa invoked from kernel context!", regs);
err = enable_restore_fp_context(1);
if (err)
force_sig(SIGILL, current);
out:
exception_exit(prev_state);
}
asmlinkage void do_mdmx(struct pt_regs *regs)
{
enum ctx_state prev_state;
@ -2041,6 +2129,7 @@ void __init trap_init(void)
set_except_vector(15, handle_fpe);
set_except_vector(16, handle_ftlb);
set_except_vector(21, handle_msa);
set_except_vector(22, handle_mdmx);
if (cpu_has_mcheck)