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Commit faea6234 authored by Atsushi Nemoto's avatar Atsushi Nemoto Committed by Ralf Baechle
Browse files

[MIPS] Retry {save,restore}_fp_context if failed in atomic context. 



The save_fp_context()/restore_fp_context() might sleep on accessing
user stack and therefore might lose FPU ownership in middle of them.

If these function failed due to "in_atomic" test in do_page_fault,
touch the sigcontext area in non-atomic context and retry these
save/restore operation.

This is a replacement of a (broken) fix which was titled "Allow CpU
exception in kernel partially".

Signed-off-by: default avatarAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 5323180d

arch/mips/kernel/signal-common.h

+9 −0
Original line number Diff line number Diff line
@@ -34,4 +34,13 @@ extern int install_sigtramp(unsigned int __user *tramp, unsigned int syscall); 
/* Check and clear pending FPU exceptions in saved CSR */

extern int fpcsr_pending(unsigned int __user *fpcsr);



/* Make sure we will not lose FPU ownership */

#ifdef CONFIG_PREEMPT

#define lock_fpu_owner()	preempt_disable()

#define unlock_fpu_owner()	preempt_enable()

#else

#define lock_fpu_owner()	pagefault_disable()

#define unlock_fpu_owner()	pagefault_enable()

#endif



#endif	/* __SIGNAL_COMMON_H */

arch/mips/kernel/signal.c

+43 −9
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <linux/ptrace.h>

#include <linux/unistd.h>

#include <linux/compiler.h>

#include <linux/uaccess.h>



#include <asm/abi.h>

#include <asm/asm.h>
@@ -27,7 +28,6 @@ 
#include <asm/cacheflush.h>

#include <asm/fpu.h>

#include <asm/sim.h>

#include <asm/uaccess.h>

#include <asm/ucontext.h>

#include <asm/cpu-features.h>

#include <asm/war.h>
@@ -78,6 +78,46 @@ struct rt_sigframe { 
/*

 * Helper routines

 */

static int protected_save_fp_context(struct sigcontext __user *sc)

{

	int err;

	while (1) {

		lock_fpu_owner();

		own_fpu_inatomic(1);

		err = save_fp_context(sc); /* this might fail */

		unlock_fpu_owner();

		if (likely(!err))

			break;

		/* touch the sigcontext and try again */

		err = __put_user(0, &sc->sc_fpregs[0]) |

			__put_user(0, &sc->sc_fpregs[31]) |

			__put_user(0, &sc->sc_fpc_csr);

		if (err)

			break;	/* really bad sigcontext */

	}

	return err;

}



static int protected_restore_fp_context(struct sigcontext __user *sc)

{

	int err, tmp;

	while (1) {

		lock_fpu_owner();

		own_fpu_inatomic(0);

		err = restore_fp_context(sc); /* this might fail */

		unlock_fpu_owner();

		if (likely(!err))

			break;

		/* touch the sigcontext and try again */

		err = __get_user(tmp, &sc->sc_fpregs[0]) |

			__get_user(tmp, &sc->sc_fpregs[31]) |

			__get_user(tmp, &sc->sc_fpc_csr);

		if (err)

			break;	/* really bad sigcontext */

	}

	return err;

}



int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)

{

	int err = 0;
@@ -113,10 +153,7 @@ int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc) 
		 * Save FPU state to signal context. Signal handler

		 * will "inherit" current FPU state.

		 */

		preempt_disable();

		own_fpu(1);

		err |= save_fp_context(sc);

		preempt_enable();

		err |= protected_save_fp_context(sc);

	}

	return err;

}
@@ -148,10 +185,7 @@ check_and_restore_fp_context(struct sigcontext __user *sc) 
	err = sig = fpcsr_pending(&sc->sc_fpc_csr);

	if (err > 0)

		err = 0;

	preempt_disable();

	own_fpu(0);

	err |= restore_fp_context(sc);

	preempt_enable();

	err |= protected_restore_fp_context(sc);

	return err ?: sig;

}

arch/mips/kernel/signal32.c

+43 −9
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <linux/compat.h>

#include <linux/suspend.h>

#include <linux/compiler.h>

#include <linux/uaccess.h>



#include <asm/abi.h>

#include <asm/asm.h>
@@ -29,7 +30,6 @@ 
#include <linux/bitops.h>

#include <asm/cacheflush.h>

#include <asm/sim.h>

#include <asm/uaccess.h>

#include <asm/ucontext.h>

#include <asm/system.h>

#include <asm/fpu.h>
@@ -176,6 +176,46 @@ struct rt_sigframe32 { 
/*

 * sigcontext handlers

 */

static int protected_save_fp_context32(struct sigcontext32 __user *sc)

{

	int err;

	while (1) {

		lock_fpu_owner();

		own_fpu_inatomic(1);

		err = save_fp_context32(sc); /* this might fail */

		unlock_fpu_owner();

		if (likely(!err))

			break;

		/* touch the sigcontext and try again */

		err = __put_user(0, &sc->sc_fpregs[0]) |

			__put_user(0, &sc->sc_fpregs[31]) |

			__put_user(0, &sc->sc_fpc_csr);

		if (err)

			break;	/* really bad sigcontext */

	}

	return err;

}



static int protected_restore_fp_context32(struct sigcontext32 __user *sc)

{

	int err, tmp;

	while (1) {

		lock_fpu_owner();

		own_fpu_inatomic(0);

		err = restore_fp_context32(sc); /* this might fail */

		unlock_fpu_owner();

		if (likely(!err))

			break;

		/* touch the sigcontext and try again */

		err = __get_user(tmp, &sc->sc_fpregs[0]) |

			__get_user(tmp, &sc->sc_fpregs[31]) |

			__get_user(tmp, &sc->sc_fpc_csr);

		if (err)

			break;	/* really bad sigcontext */

	}

	return err;

}



static int setup_sigcontext32(struct pt_regs *regs,

			      struct sigcontext32 __user *sc)

{
@@ -209,10 +249,7 @@ static int setup_sigcontext32(struct pt_regs *regs, 
		 * Save FPU state to signal context.  Signal handler

		 * will "inherit" current FPU state.

		 */

		preempt_disable();

		own_fpu(1);

		err |= save_fp_context32(sc);

		preempt_enable();

		err |= protected_save_fp_context32(sc);

	}

	return err;

}
@@ -225,10 +262,7 @@ check_and_restore_fp_context32(struct sigcontext32 __user *sc) 
	err = sig = fpcsr_pending(&sc->sc_fpc_csr);

	if (err > 0)

		err = 0;

	preempt_disable();

	own_fpu(0);

	err |= restore_fp_context32(sc);

	preempt_enable();

	err |= protected_restore_fp_context32(sc);

	return err ?: sig;

}

include/asm-mips/fpu.h

+7 −2
Original line number Diff line number Diff line
@@ -100,14 +100,19 @@ static inline void __own_fpu(void) 
	set_thread_flag(TIF_USEDFPU);

}



static inline void own_fpu(int restore)

static inline void own_fpu_inatomic(int restore)

{

	preempt_disable();

	if (cpu_has_fpu && !__is_fpu_owner()) {

		__own_fpu();

		if (restore)

			_restore_fp(current);

	}

}



static inline void own_fpu(int restore)

{

	preempt_disable();

	own_fpu_inatomic(restore);

	preempt_enable();

}