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