From: Vincent Chen <vincent.chen@xxxxxxxxxx>
commit 8ac71d7e46b94a4fc8ffc6f1c88004cdf24459e8 upstream.
The following two reasons cause FP registers are sometimes not
initialized before starting the user program.
1. Currently, the FP context is initialized in flush_thread() function
and we expect these initial values to be restored to FP register when
doing FP context switch. However, the FP context switch only occurs in
switch_to function. Hence, if this process does not be scheduled out
and scheduled in before entering the user space, the FP registers
have no chance to initialize.
2. In flush_thread(), the state of reg->sstatus.FS inherits from the
parent. Hence, the state of reg->sstatus.FS may be dirty. If this
process is scheduled out during flush_thread() and initializing the
FP register, the fstate_save() in switch_to will corrupt the FP context
which has been initialized until flush_thread().
To solve the 1st case, the initialization of the FP register will be
completed in start_thread(). It makes sure all FP registers are initialized
before starting the user program. For the 2nd case, the state of
reg->sstatus.FS in start_thread will be set to SR_FS_OFF to prevent this
process from corrupting FP context in doing context save. The FP state is
set to SR_FS_INITIAL in start_trhead().
Signed-off-by: Vincent Chen <vincent.chen@xxxxxxxxxx>
Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Fixes: 7db91e57a0acd ("RISC-V: Task implementation")
Cc: stable@xxxxxxxxxxxxxxx
[paul.walmsley@xxxxxxxxxx: fixed brace alignment issue reported by
checkpatch]
Signed-off-by: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/riscv/include/asm/switch_to.h | 6 ++++++
arch/riscv/kernel/process.c | 11 +++++++++--
2 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 853b65ef656da..949d9cd91dec4 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -19,6 +19,12 @@ static inline void __fstate_clean(struct pt_regs *regs)
regs->sstatus |= (regs->sstatus & ~(SR_FS)) | SR_FS_CLEAN;
}
+static inline void fstate_off(struct task_struct *task,
+ struct pt_regs *regs)
+{
+ regs->sstatus = (regs->sstatus & ~SR_FS) | SR_FS_OFF;
+}
+
static inline void fstate_save(struct task_struct *task,
struct pt_regs *regs)
{
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index f23794bd1e90c..fb3a082362eb8 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -64,8 +64,14 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
unsigned long sp)
{
regs->sstatus = SR_SPIE;
- if (has_fpu)
+ if (has_fpu) {
regs->sstatus |= SR_FS_INITIAL;
+ /*
+ * Restore the initial value to the FP register
+ * before starting the user program.
+ */
+ fstate_restore(current, regs);
+ }
regs->sepc = pc;
regs->sp = sp;
set_fs(USER_DS);
@@ -75,10 +81,11 @@ void flush_thread(void)
{
#ifdef CONFIG_FPU
/*
- * Reset FPU context
+ * Reset FPU state and context
* frm: round to nearest, ties to even (IEEE default)
* fflags: accrued exceptions cleared
*/
+ fstate_off(current, task_pt_regs(current));
memset(¤t->thread.fstate, 0, sizeof(current->thread.fstate));
#endif
}
--
2.20.1
