In v4.16-RT I noticed a number of warnings from task_fpsimd_load(). The
code disables BH and expects that it is not preemptible. On -RT the
task remains preemptible but remains the same CPU. This may corrupt the
content of the SIMD registers if the task is preempted during
saving/restoring those registers.
Add preempt_disable()/enable() to enfore the required semantic on -RT.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
This should work. Compiling currently gcc-6 on the box to see what
happens. Since the crypto disables preemption "frequently" and I don't
expect or see anything to worry about.
arch/arm64/kernel/fpsimd.c | 30 ++++++++++++++++++++++++++++--
1 file changed, 28 insertions(+), 2 deletions(-)
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -157,6 +157,15 @@ static void sve_free(struct task_struct
__sve_free(task);
}
+static void *sve_free_atomic(struct task_struct *task)
+{
+ void *sve_state = task->thread.sve_state;
+
+ WARN_ON(test_tsk_thread_flag(task, TIF_SVE));
+
+ task->thread.sve_state = NULL;
+ return sve_state;
+}
/* Offset of FFR in the SVE register dump */
static size_t sve_ffr_offset(int vl)
@@ -594,6 +603,7 @@ int sve_set_vector_length(struct task_st
* non-SVE thread.
*/
if (task == current) {
+ preempt_disable();
local_bh_disable();
task_fpsimd_save();
@@ -604,8 +614,10 @@ int sve_set_vector_length(struct task_st
if (test_and_clear_tsk_thread_flag(task, TIF_SVE))
sve_to_fpsimd(task);
- if (task == current)
+ if (task == current) {
local_bh_enable();
+ preempt_enable();
+ }
/*
* Force reallocation of task SVE state to the correct size
@@ -837,6 +849,7 @@ asmlinkage void do_sve_acc(unsigned int
sve_alloc(current);
+ preempt_disable();
local_bh_disable();
task_fpsimd_save();
@@ -850,6 +863,7 @@ asmlinkage void do_sve_acc(unsigned int
WARN_ON(1); /* SVE access shouldn't have trapped */
local_bh_enable();
+ preempt_enable();
}
/*
@@ -921,10 +935,12 @@ void fpsimd_thread_switch(struct task_st
void fpsimd_flush_thread(void)
{
int vl, supported_vl;
+ void *mem = NULL;
if (!system_supports_fpsimd())
return;
+ preempt_disable();
local_bh_disable();
memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
@@ -932,7 +948,7 @@ void fpsimd_flush_thread(void)
if (system_supports_sve()) {
clear_thread_flag(TIF_SVE);
- sve_free(current);
+ mem = sve_free_atomic(current);
/*
* Reset the task vector length as required.
@@ -968,6 +984,8 @@ void fpsimd_flush_thread(void)
set_thread_flag(TIF_FOREIGN_FPSTATE);
local_bh_enable();
+ preempt_enable();
+ kfree(mem);
}
/*
@@ -979,9 +997,11 @@ void fpsimd_preserve_current_state(void)
if (!system_supports_fpsimd())
return;
+ preempt_disable();
local_bh_disable();
task_fpsimd_save();
local_bh_enable();
+ preempt_enable();
}
/*
@@ -1021,6 +1041,7 @@ void fpsimd_restore_current_state(void)
if (!system_supports_fpsimd())
return;
+ preempt_disable();
local_bh_disable();
if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
@@ -1029,6 +1050,7 @@ void fpsimd_restore_current_state(void)
}
local_bh_enable();
+ preempt_enable();
}
/*
@@ -1041,6 +1063,7 @@ void fpsimd_update_current_state(struct
if (!system_supports_fpsimd())
return;
+ preempt_disable();
local_bh_disable();
current->thread.fpsimd_state.user_fpsimd = *state;
@@ -1053,6 +1076,7 @@ void fpsimd_update_current_state(struct
fpsimd_bind_to_cpu();
local_bh_enable();
+ preempt_enable();
}
/*
@@ -1115,6 +1139,7 @@ void kernel_neon_begin(void)
BUG_ON(!may_use_simd());
+ preempt_disable();
local_bh_disable();
__this_cpu_write(kernel_neon_busy, true);
@@ -1131,6 +1156,7 @@ void kernel_neon_begin(void)
preempt_disable();
local_bh_enable();
+ preempt_enable();
}
EXPORT_SYMBOL(kernel_neon_begin);
--
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