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8ac71d7e46
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@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Fixes: 7db91e57a0 ("RISC-V: Task implementation")
Cc: stable@vger.kernel.org
[paul.walmsley@sifive.com: fixed brace alignment issue reported by
checkpatch]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
128 lines
3.6 KiB
C
128 lines
3.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2009 Sunplus Core Technology Co., Ltd.
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* Chen Liqin <liqin.chen@sunplusct.com>
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* Lennox Wu <lennox.wu@sunplusct.com>
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* Copyright (C) 2012 Regents of the University of California
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* Copyright (C) 2017 SiFive
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*/
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/sched/task_stack.h>
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#include <linux/tick.h>
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#include <linux/ptrace.h>
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#include <linux/uaccess.h>
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#include <asm/unistd.h>
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#include <asm/processor.h>
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#include <asm/csr.h>
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#include <asm/string.h>
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#include <asm/switch_to.h>
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extern asmlinkage void ret_from_fork(void);
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extern asmlinkage void ret_from_kernel_thread(void);
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void arch_cpu_idle(void)
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{
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wait_for_interrupt();
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local_irq_enable();
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}
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void show_regs(struct pt_regs *regs)
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{
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show_regs_print_info(KERN_DEFAULT);
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pr_cont("sepc: " REG_FMT " ra : " REG_FMT " sp : " REG_FMT "\n",
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regs->sepc, regs->ra, regs->sp);
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pr_cont(" gp : " REG_FMT " tp : " REG_FMT " t0 : " REG_FMT "\n",
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regs->gp, regs->tp, regs->t0);
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pr_cont(" t1 : " REG_FMT " t2 : " REG_FMT " s0 : " REG_FMT "\n",
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regs->t1, regs->t2, regs->s0);
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pr_cont(" s1 : " REG_FMT " a0 : " REG_FMT " a1 : " REG_FMT "\n",
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regs->s1, regs->a0, regs->a1);
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pr_cont(" a2 : " REG_FMT " a3 : " REG_FMT " a4 : " REG_FMT "\n",
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regs->a2, regs->a3, regs->a4);
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pr_cont(" a5 : " REG_FMT " a6 : " REG_FMT " a7 : " REG_FMT "\n",
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regs->a5, regs->a6, regs->a7);
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pr_cont(" s2 : " REG_FMT " s3 : " REG_FMT " s4 : " REG_FMT "\n",
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regs->s2, regs->s3, regs->s4);
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pr_cont(" s5 : " REG_FMT " s6 : " REG_FMT " s7 : " REG_FMT "\n",
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regs->s5, regs->s6, regs->s7);
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pr_cont(" s8 : " REG_FMT " s9 : " REG_FMT " s10: " REG_FMT "\n",
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regs->s8, regs->s9, regs->s10);
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pr_cont(" s11: " REG_FMT " t3 : " REG_FMT " t4 : " REG_FMT "\n",
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regs->s11, regs->t3, regs->t4);
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pr_cont(" t5 : " REG_FMT " t6 : " REG_FMT "\n",
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regs->t5, regs->t6);
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pr_cont("sstatus: " REG_FMT " sbadaddr: " REG_FMT " scause: " REG_FMT "\n",
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regs->sstatus, regs->sbadaddr, regs->scause);
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}
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void start_thread(struct pt_regs *regs, unsigned long pc,
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unsigned long sp)
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{
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regs->sstatus = SR_SPIE;
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if (has_fpu) {
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regs->sstatus |= SR_FS_INITIAL;
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/*
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* Restore the initial value to the FP register
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* before starting the user program.
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*/
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fstate_restore(current, regs);
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}
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regs->sepc = pc;
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regs->sp = sp;
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set_fs(USER_DS);
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}
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void flush_thread(void)
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{
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#ifdef CONFIG_FPU
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/*
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* Reset FPU state and context
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* frm: round to nearest, ties to even (IEEE default)
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* fflags: accrued exceptions cleared
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*/
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fstate_off(current, task_pt_regs(current));
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memset(¤t->thread.fstate, 0, sizeof(current->thread.fstate));
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#endif
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}
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int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
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{
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fstate_save(src, task_pt_regs(src));
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*dst = *src;
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return 0;
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}
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int copy_thread(unsigned long clone_flags, unsigned long usp,
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unsigned long arg, struct task_struct *p)
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{
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struct pt_regs *childregs = task_pt_regs(p);
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/* p->thread holds context to be restored by __switch_to() */
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if (unlikely(p->flags & PF_KTHREAD)) {
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/* Kernel thread */
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const register unsigned long gp __asm__ ("gp");
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memset(childregs, 0, sizeof(struct pt_regs));
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childregs->gp = gp;
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childregs->sstatus = SR_SPP | SR_SPIE; /* Supervisor, irqs on */
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p->thread.ra = (unsigned long)ret_from_kernel_thread;
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p->thread.s[0] = usp; /* fn */
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p->thread.s[1] = arg;
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} else {
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*childregs = *(current_pt_regs());
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if (usp) /* User fork */
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childregs->sp = usp;
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if (clone_flags & CLONE_SETTLS)
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childregs->tp = childregs->a5;
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childregs->a0 = 0; /* Return value of fork() */
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p->thread.ra = (unsigned long)ret_from_fork;
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}
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p->thread.sp = (unsigned long)childregs; /* kernel sp */
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return 0;
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}
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