MIPS: Always clear FCSR cause bits after emulation

Clear any FCSR cause bits recorded in the saved FPU context after
emulation in all cases rather than in `do_fpe' only, so that any
unmasked IEEE 754 exception left from emulation does not cause a fatal
kernel-mode FPE hardware exception with the CTC1 instruction used by the
kernel to subsequently restore FCSR hardware from the saved FPU context.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9704/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/mips-r2-to-r6-emul.c b/arch/mips/kernel/mips-r2-to-r6-emul.c
index f1d1b42..6633fa9 100644 (file)
--- a/arch/mips/kernel/mips-r2-to-r6-emul.c
+++ b/arch/mips/kernel/mips-r2-to-r6-emul.c
@@ -1170,6 +1170,12 @@ fpu_emul:
                                               &fault_addr);
 
                /*
+                * We can't allow the emulated instruction to leave any of
+                * the cause bits set in $fcr31.
+                */
+               current->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
+
+               /*
                 * this is a tricky issue - lose_fpu() uses LL/SC atomics
                 * if FPU is owned and effectively cancels user level LL/SC.
                 * So, it could be logical to don't restore FPU ownership here.

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index dbfa47c..4a0552d 100644 (file)
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -761,6 +761,12 @@ static int simulate_fp(struct pt_regs *regs, unsigned int opcode,
        sig = fpu_emulator_cop1Handler(regs, &current->thread.fpu, 1,
                                       &fault_addr);
 
+       /*
+        * We can't allow the emulated instruction to leave any of
+        * the cause bits set in $fcr31.
+        */
+       current->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
+
        /* If something went wrong, signal */
        process_fpemu_return(sig, fault_addr);
 
@@ -807,7 +813,7 @@ asmlinkage void do_fpe(struct pt_regs *regs, unsigned long fcr31)
 
                /*
                 * We can't allow the emulated instruction to leave any of
-                * the cause bit set in $fcr31.
+                * the cause bits set in $fcr31.
                 */
                current->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
 
@@ -1384,6 +1390,13 @@ asmlinkage void do_cpu(struct pt_regs *regs)
                        sig = fpu_emulator_cop1Handler(regs,
                                                       &current->thread.fpu,
                                                       0, &fault_addr);
+
+                       /*
+                        * We can't allow the emulated instruction to leave
+                        * any of the cause bits set in $fcr31.
+                        */
+                       current->thread.fpu.fcr31 &= ~FPU_CSR_ALL_X;
+
                        if (!process_fpemu_return(sig, fault_addr) && !err)
                                mt_ase_fp_affinity();
                }