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Re: [PATCH] Disallow CpU exception in kernel again.

To: linux-mips@linux-mips.org
Subject: Re: [PATCH] Disallow CpU exception in kernel again.
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Sat, 14 Apr 2007 02:44:50 +0900 (JST)
Cc: ralf@linux-mips.org
In-reply-to: <20070414.023726.128617751.anemo@mba.ocn.ne.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20070414.022143.82357892.anemo@mba.ocn.ne.jp> <20070414.023726.128617751.anemo@mba.ocn.ne.jp>
Sender: linux-mips-bounce@linux-mips.org
On Sat, 14 Apr 2007 02:37:26 +0900 (JST), Atsushi Nemoto <anemo@mba.ocn.ne.jp> 
wrote:
> Subject: [PATCH] Disallow CpU exception in kernel again.
> 
> The commit 4d40bff7110e9e1a97ff8c01bdd6350e9867cc10 ("Allow CpU
> exception in kernel partially") was broken.  The commit was to fix
> theoretical problem but broke usual case.  Revert it for now.
> 
> Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>

And this is for 2.6.20-stable.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
---
 arch/mips/kernel/r2300_switch.S  |   10 ++++------
 arch/mips/kernel/r4k_switch.S    |   10 ++++------
 arch/mips/kernel/signal-common.h |   10 +++++-----
 arch/mips/kernel/signal32.c      |   10 +++++-----
 arch/mips/kernel/traps.c         |   21 +++------------------
 include/asm-mips/fpu.h           |   16 ----------------
 include/asm-mips/thread_info.h   |    1 -
 7 files changed, 21 insertions(+), 57 deletions(-)

diff --git a/arch/mips/kernel/r2300_switch.S b/arch/mips/kernel/r2300_switch.S
index 28c2e2e..656bde2 100644
--- a/arch/mips/kernel/r2300_switch.S
+++ b/arch/mips/kernel/r2300_switch.S
@@ -49,7 +49,8 @@ LEAF(resume)
 #ifndef CONFIG_CPU_HAS_LLSC
        sw      zero, ll_bit
 #endif
-       mfc0    t2, CP0_STATUS
+       mfc0    t1, CP0_STATUS
+       sw      t1, THREAD_STATUS(a0)
        cpu_save_nonscratch a0
        sw      ra, THREAD_REG31(a0)
 
@@ -59,8 +60,8 @@ LEAF(resume)
        lw      t3, TASK_THREAD_INFO(a0)
        lw      t0, TI_FLAGS(t3)
        li      t1, _TIF_USEDFPU
-       and     t1, t0
-       beqz    t1, 1f
+       and     t2, t0, t1
+       beqz    t2, 1f
        nor     t1, zero, t1
 
        and     t0, t0, t1
@@ -73,13 +74,10 @@ LEAF(resume)
        li      t1, ~ST0_CU1
        and     t0, t0, t1
        sw      t0, ST_OFF(t3)
-       /* clear thread_struct CU1 bit */
-       and     t2, t1
 
        fpu_save_single a0, t0                  # clobbers t0
 
 1:
-       sw      t2, THREAD_STATUS(a0)
        /*
         * The order of restoring the registers takes care of the race
         * updating $28, $29 and kernelsp without disabling ints.
diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S
index c7698fd..cc566cf 100644
--- a/arch/mips/kernel/r4k_switch.S
+++ b/arch/mips/kernel/r4k_switch.S
@@ -48,7 +48,8 @@
 #ifndef CONFIG_CPU_HAS_LLSC
        sw      zero, ll_bit
 #endif
-       mfc0    t2, CP0_STATUS
+       mfc0    t1, CP0_STATUS
+       LONG_S  t1, THREAD_STATUS(a0)
        cpu_save_nonscratch a0
        LONG_S  ra, THREAD_REG31(a0)
 
@@ -58,8 +59,8 @@
        PTR_L   t3, TASK_THREAD_INFO(a0)
        LONG_L  t0, TI_FLAGS(t3)
        li      t1, _TIF_USEDFPU
-       and     t1, t0
-       beqz    t1, 1f
+       and     t2, t0, t1
+       beqz    t2, 1f
        nor     t1, zero, t1
 
        and     t0, t0, t1
@@ -72,13 +73,10 @@
        li      t1, ~ST0_CU1
        and     t0, t0, t1
        LONG_S  t0, ST_OFF(t3)
-       /* clear thread_struct CU1 bit */
-       and     t2, t1
 
        fpu_save_double a0 t0 t1                # c0_status passed in t0
                                                # clobbers t1
 1:
-       LONG_S  t2, THREAD_STATUS(a0)
 
        /*
         * The order of restoring the registers takes care of the race
diff --git a/arch/mips/kernel/signal-common.h b/arch/mips/kernel/signal-common.h
index 87d8320..b625e9c 100644
--- a/arch/mips/kernel/signal-common.h
+++ b/arch/mips/kernel/signal-common.h
@@ -51,10 +51,10 @@ setup_sigcontext(struct pt_regs *regs, s
         * Save FPU state to signal context.  Signal handler will "inherit"
         * current FPU state.
         */
+       preempt_disable();
        own_fpu(1);
-       enable_fp_in_kernel();
        err |= save_fp_context(sc);
-       disable_fp_in_kernel();
+       preempt_enable();
 
 out:
        return err;
@@ -71,7 +71,10 @@ check_and_restore_fp_context(struct sigc
        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();
        return err ?: sig;
 }
 
@@ -119,11 +122,8 @@ restore_sigcontext(struct pt_regs *regs,
 
        if (used_math()) {
                /* restore fpu context if we have used it before */
-               own_fpu(0);
-               enable_fp_in_kernel();
                if (!err)
                        err = check_and_restore_fp_context(sc);
-               disable_fp_in_kernel();
        } else {
                /* signal handler may have used FPU.  Give it up. */
                lose_fpu(0);
diff --git a/arch/mips/kernel/signal32.c b/arch/mips/kernel/signal32.c
index 4a32f99..1a3f541 100644
--- a/arch/mips/kernel/signal32.c
+++ b/arch/mips/kernel/signal32.c
@@ -145,7 +145,10 @@ check_and_restore_fp_context32(struct si
        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();
        return err ?: sig;
 }
 
@@ -379,11 +382,8 @@ static int restore_sigcontext32(struct p
 
        if (used_math()) {
                /* restore fpu context if we have used it before */
-               own_fpu(0);
-               enable_fp_in_kernel();
                if (!err)
                        err = check_and_restore_fp_context32(sc);
-               disable_fp_in_kernel();
        } else {
                /* signal handler may have used FPU.  Give it up. */
                lose_fpu(0);
@@ -614,10 +614,10 @@ static inline int setup_sigcontext32(str
         * Save FPU state to signal context.  Signal handler will "inherit"
         * current FPU state.
         */
+       preempt_disable();
        own_fpu(1);
-       enable_fp_in_kernel();
        err |= save_fp_context32(sc);
-       disable_fp_in_kernel();
+       preempt_enable();
 
 out:
        return err;
diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index afb09e8..64b9dfb 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -758,11 +758,12 @@ asmlinkage void do_cpu(struct pt_regs *r
 {
        unsigned int cpid;
 
+       die_if_kernel("do_cpu invoked from kernel context!", regs);
+
        cpid = (regs->cp0_cause >> CAUSEB_CE) & 3;
 
        switch (cpid) {
        case 0:
-               die_if_kernel("do_cpu invoked from kernel context!", regs);
                if (!cpu_has_llsc)
                        if (!simulate_llsc(regs))
                                return;
@@ -773,9 +774,6 @@ asmlinkage void do_cpu(struct pt_regs *r
                break;
 
        case 1:
-               if (!test_thread_flag(TIF_ALLOW_FP_IN_KERNEL))
-                       die_if_kernel("do_cpu invoked from kernel context!",
-                                     regs);
                if (used_math())        /* Using the FPU again.  */
                        own_fpu(1);
                else {                  /* First time FPU user.  */
@@ -783,19 +781,7 @@ asmlinkage void do_cpu(struct pt_regs *r
                        set_used_math();
                }
 
-               if (raw_cpu_has_fpu) {
-                       if (test_thread_flag(TIF_ALLOW_FP_IN_KERNEL)) {
-                               local_irq_disable();
-                               if (cpu_has_fpu)
-                                       regs->cp0_status |= ST0_CU1;
-                               /*
-                                * We must return without enabling
-                                * interrupts to ensure keep FPU
-                                * ownership until resume.
-                                */
-                               return;
-                       }
-               } else {
+               if (!raw_cpu_has_fpu) {
                        int sig;
                        sig = fpu_emulator_cop1Handler(regs,
                                                &current->thread.fpu, 0);
@@ -837,7 +823,6 @@ asmlinkage void do_cpu(struct pt_regs *r
 
        case 2:
        case 3:
-               die_if_kernel("do_cpu invoked from kernel context!", regs);
                break;
        }
 
diff --git a/include/asm-mips/fpu.h b/include/asm-mips/fpu.h
index dfecb7b..6b9d1bf 100644
--- a/include/asm-mips/fpu.h
+++ b/include/asm-mips/fpu.h
@@ -68,8 +68,6 @@ do {                                                          
        \
        /* We don't care about the c0 hazard here  */                   \
 } while (0)
 
-#define __fpu_enabled()        (read_c0_status() & ST0_CU1)
-
 #define enable_fpu()                                                   \
 do {                                                                   \
        if (cpu_has_fpu)                                                \
@@ -162,18 +160,4 @@ static inline fpureg_t *get_fpu_regs(str
        return tsk->thread.fpu.fpr;
 }
 
-static inline void enable_fp_in_kernel(void)
-{
-       set_thread_flag(TIF_ALLOW_FP_IN_KERNEL);
-       /* make sure CU1 and FPU ownership are consistent */
-       if (!__is_fpu_owner() && __fpu_enabled())
-               __disable_fpu();
-}
-
-static inline void disable_fp_in_kernel(void)
-{
-       BUG_ON(!__is_fpu_owner() && __fpu_enabled());
-       clear_thread_flag(TIF_ALLOW_FP_IN_KERNEL);
-}
-
 #endif /* _ASM_FPU_H */
diff --git a/include/asm-mips/thread_info.h b/include/asm-mips/thread_info.h
index 6cf05f4..fbcda82 100644
--- a/include/asm-mips/thread_info.h
+++ b/include/asm-mips/thread_info.h
@@ -119,7 +119,6 @@ register struct thread_info *__current_t
 #define TIF_POLLING_NRFLAG     17      /* true if poll_idle() is polling 
TIF_NEED_RESCHED */
 #define TIF_MEMDIE             18
 #define TIF_FREEZE             19
-#define TIF_ALLOW_FP_IN_KERNEL 20
 #define TIF_SYSCALL_TRACE      31      /* syscall trace active */
 
 #define _TIF_SYSCALL_TRACE     (1<<TIF_SYSCALL_TRACE)

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