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Commit 1d74f6bc authored by Ralf Baechle's avatar Ralf Baechle
Browse files

__compute_return_epc() uses CFC1 instruction which might result in a 


coprocessor unusable exception since the process can lose its fpu
context by preemption.

Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent d547c5cc

arch/mips/kernel/branch.c

+7 −3
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ 
#include <asm/branch.h>

#include <asm/cpu.h>

#include <asm/cpu-features.h>

#include <asm/fpu.h>

#include <asm/inst.h>

#include <asm/ptrace.h>

#include <asm/uaccess.h>
@@ -161,10 +162,13 @@ int __compute_return_epc(struct pt_regs *regs) 
	 * And now the FPA/cp1 branch instructions.

	 */

	case cop1_op:

		if (!cpu_has_fpu)

			fcr31 = current->thread.fpu.soft.fcr31;

		else

		preempt_disable();

		if (is_fpu_owner())

			asm volatile("cfc1\t%0,$31" : "=r" (fcr31));

		else

			fcr31 = current->thread.fpu.hard.fcr31;

		preempt_enable();



		bit = (insn.i_format.rt >> 2);

		bit += (bit != 0);

		bit += 23;

include/asm-mips/fpu.h

+7 −2
Original line number Diff line number Diff line
@@ -80,9 +80,14 @@ do { \ 


#define clear_fpu_owner()	clear_thread_flag(TIF_USEDFPU)



static inline int __is_fpu_owner(void)

{

	return test_thread_flag(TIF_USEDFPU);

}



static inline int is_fpu_owner(void)

{

	return cpu_has_fpu && test_thread_flag(TIF_USEDFPU);

	return cpu_has_fpu && __is_fpu_owner();

}



static inline void own_fpu(void)
@@ -127,7 +132,7 @@ static inline void restore_fp(struct task_struct *tsk) 
static inline fpureg_t *get_fpu_regs(struct task_struct *tsk)

{

	if (cpu_has_fpu) {

		if ((tsk == current) && is_fpu_owner())

		if ((tsk == current) && __is_fpu_owner())

			_save_fp(current);

		return tsk->thread.fpu.hard.fpr;

	}