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Revert "arm64: defer reloading a task's FPSIMD state to userland resume"

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This reverts commit 41f7d22a9e.

This change results in occasional userspace crashes, presumably because
incorrect FPSIMD state is saved/restored. Revert it until the problems
are understood and fixed, resolving several merge conflicts along the
way.

Change-Id: I030c413950640aa6b83d55a8af5f75ab54ab9b7e
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
This commit is contained in:
Matt Wagantall 2014-08-21 22:07:01 -07:00
parent a202b02196
commit 115a3dc50c
6 changed files with 16 additions and 135 deletions
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5
arch/arm64/include/asm/fpsimd.h
View file

@ -37,8 +37,6 @@ struct fpsimd_state {
u32 fpcr;
};
};
/* the id of the last cpu to have restored this state */
unsigned int cpu;
};
/*
@ -72,11 +70,8 @@ extern void fpsimd_thread_switch(struct task_struct *next);
extern void fpsimd_flush_thread(void);
extern void fpsimd_preserve_current_state(void);
extern void fpsimd_restore_current_state(void);
extern void fpsimd_update_current_state(struct fpsimd_state *state);
extern void fpsimd_flush_task_state(struct task_struct *target);
extern void fpsimd_save_partial_state(struct fpsimd_partial_state *state,
u32 num_regs);
extern void fpsimd_load_partial_state(struct fpsimd_partial_state *state);

4
arch/arm64/include/asm/thread_info.h
View file

@ -108,7 +108,6 @@ static inline struct thread_info *current_thread_info(void)
#define TIF_SIGPENDING 0
#define TIF_NEED_RESCHED 1
#define TIF_NOTIFY_RESUME 2 /* callback before returning to user */
#define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */
#define TIF_SYSCALL_TRACE 8
#define TIF_SYSCALL_AUDIT 9
#define TIF_SYSCALL_TRACEPOINT 10
@ -124,7 +123,6 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_SIGPENDING (1 << TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE)
#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
#define _TIF_SYSCALL_TRACEPOINT (1 << TIF_SYSCALL_TRACEPOINT)
@ -132,7 +130,7 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_32BIT (1 << TIF_32BIT)
#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
_TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE)
_TIF_NOTIFY_RESUME)
#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP)

2
arch/arm64/kernel/entry.S
View file

@ -566,7 +566,7 @@ fast_work_pending:
str x0, [sp, #S_X0] // returned x0
work_pending:
tbnz x1, #TIF_NEED_RESCHED, work_resched
/* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */
/* TIF_SIGPENDING or TIF_NOTIFY_RESUME case */
ldr x2, [sp, #S_PSTATE]
mov x0, sp // 'regs'
tst x2, #PSR_MODE_MASK // user mode regs?

134
arch/arm64/kernel/fpsimd.c
View file

@ -34,59 +34,6 @@
#define FPEXC_IXF (1 << 4)
#define FPEXC_IDF (1 << 7)
/*
* In order to reduce the number of times the FPSIMD state is needlessly saved
* and restored, we need to keep track of two things:
* (a) for each task, we need to remember which CPU was the last one to have
* the task's FPSIMD state loaded into its FPSIMD registers;
* (b) for each CPU, we need to remember which task's userland FPSIMD state has
* been loaded into its FPSIMD registers most recently, or whether it has
* been used to perform kernel mode NEON in the meantime.
*
* For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
* the id of the current CPU everytime the state is loaded onto a CPU. For (b),
* we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
* address of the userland FPSIMD state of the task that was loaded onto the CPU
* the most recently, or NULL if kernel mode NEON has been performed after that.
*
* With this in place, we no longer have to restore the next FPSIMD state right
* when switching between tasks. Instead, we can defer this check to userland
* resume, at which time we verify whether the CPU's fpsimd_last_state and the
* task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
* can omit the FPSIMD restore.
*
* As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
* indicate whether or not the userland FPSIMD state of the current task is
* present in the registers. The flag is set unless the FPSIMD registers of this
* CPU currently contain the most recent userland FPSIMD state of the current
* task.
*
* For a certain task, the sequence may look something like this:
* - the task gets scheduled in; if both the task's fpsimd_state.cpu field
* contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
* variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
* cleared, otherwise it is set;
*
* - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
* userland FPSIMD state is copied from memory to the registers, the task's
* fpsimd_state.cpu field is set to the id of the current CPU, the current
* CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
* TIF_FOREIGN_FPSTATE flag is cleared;
*
* - the task executes an ordinary syscall; upon return to userland, the
* TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
* restored;
*
* - the task executes a syscall which executes some NEON instructions; this is
* preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
* register contents to memory, clears the fpsimd_last_state per-cpu variable
* and sets the TIF_FOREIGN_FPSTATE flag;
*
* - the task gets preempted after kernel_neon_end() is called; as we have not
* returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
* whatever is in the FPSIMD registers is not saved to memory, but discarded.
*/
static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
/*
* Trapped FP/ASIMD access.
@ -126,38 +73,19 @@ void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
void fpsimd_thread_switch(struct task_struct *next)
{
/*
* Save the current FPSIMD state to memory, but only if whatever is in
* the registers is in fact the most recent userland FPSIMD state of
* 'current'.
*/
if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
if (current->mm)
fpsimd_save_state(&current->thread.fpsimd_state);
if (next->mm) {
/*
* If we are switching to a task whose most recent userland
* FPSIMD state is already in the registers of *this* cpu,
* we can skip loading the state from memory. Otherwise, set
* the TIF_FOREIGN_FPSTATE flag so the state will be loaded
* upon the next return to userland.
*/
struct fpsimd_state *st = &next->thread.fpsimd_state;
if (__this_cpu_read(fpsimd_last_state) == st
&& st->cpu == smp_processor_id())
clear_ti_thread_flag(task_thread_info(next),
TIF_FOREIGN_FPSTATE);
else
set_ti_thread_flag(task_thread_info(next),
TIF_FOREIGN_FPSTATE);
}
if (next->mm)
fpsimd_load_state(&next->thread.fpsimd_state);
}
void fpsimd_flush_thread(void)
{
preempt_disable();
memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
set_thread_flag(TIF_FOREIGN_FPSTATE);
fpsimd_load_state(&current->thread.fpsimd_state);
preempt_enable();
}
/*
@ -167,55 +95,20 @@ void fpsimd_flush_thread(void)
void fpsimd_preserve_current_state(void)
{
preempt_disable();
if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
fpsimd_save_state(&current->thread.fpsimd_state);
fpsimd_save_state(&current->thread.fpsimd_state);
preempt_enable();
}
/*
* Load the userland FPSIMD state of 'current' from memory, but only if the
* FPSIMD state already held in the registers is /not/ the most recent FPSIMD
* state of 'current'
*/
void fpsimd_restore_current_state(void)
{
preempt_disable();
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
struct fpsimd_state *st = &current->thread.fpsimd_state;
fpsimd_load_state(st);
this_cpu_write(fpsimd_last_state, st);
st->cpu = smp_processor_id();
}
preempt_enable();
}
/*
* Load an updated userland FPSIMD state for 'current' from memory and set the
* flag that indicates that the FPSIMD register contents are the most recent
* FPSIMD state of 'current'
* Load an updated userland FPSIMD state for 'current' from memory
*/
void fpsimd_update_current_state(struct fpsimd_state *state)
{
preempt_disable();
fpsimd_load_state(state);
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
struct fpsimd_state *st = &current->thread.fpsimd_state;
this_cpu_write(fpsimd_last_state, st);
st->cpu = smp_processor_id();
}
preempt_enable();
}
/*
* Invalidate live CPU copies of task t's FPSIMD state
*/
void fpsimd_flush_task_state(struct task_struct *t)
{
t->thread.fpsimd_state.cpu = NR_CPUS;
}
#ifdef CONFIG_KERNEL_MODE_NEON
static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate);
@ -240,10 +133,8 @@ void kernel_neon_begin_partial(u32 num_regs)
* registers.
*/
preempt_disable();
if (current->mm &&
!test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
if (current->mm)
fpsimd_save_state(&current->thread.fpsimd_state);
this_cpu_write(fpsimd_last_state, NULL);
}
}
EXPORT_SYMBOL(kernel_neon_begin_partial);
@ -255,6 +146,9 @@ void kernel_neon_end(void)
in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
fpsimd_load_partial_state(s);
} else {
if (current->mm)
fpsimd_load_state(&current->thread.fpsimd_state);
preempt_enable();
}
}
@ -268,12 +162,12 @@ static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
{
switch (cmd) {
case CPU_PM_ENTER:
if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
if (current->mm)
fpsimd_save_state(&current->thread.fpsimd_state);
break;
case CPU_PM_EXIT:
if (current->mm)
set_thread_flag(TIF_FOREIGN_FPSTATE);
fpsimd_load_state(&current->thread.fpsimd_state);
break;
case CPU_PM_ENTER_FAILED:
default:

2
arch/arm64/kernel/ptrace.c
View file

@ -521,7 +521,6 @@ static int fpr_set(struct task_struct *target, const struct user_regset *regset,
return ret;
target->thread.fpsimd_state.user_fpsimd = newstate;
fpsimd_flush_task_state(target);
return ret;
}
@ -779,7 +778,6 @@ static int compat_vfp_set(struct task_struct *target,
uregs->fpcr = fpscr & VFP_FPSCR_CTRL_MASK;
}
fpsimd_flush_task_state(target);
return ret;
}

4
arch/arm64/kernel/signal.c
View file

@ -430,8 +430,4 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
}
if (thread_flags & _TIF_FOREIGN_FPSTATE)
fpsimd_restore_current_state();
}