commit 443c44032a54f9acf027a8e688380fddc809bc19
author Maciej W. Rozycki <macro@linux-mips.org> Fri Apr 03 23:27:10 2015 +0100
committer Ralf Baechle <ralf@linux-mips.org> Wed Apr 08 01:10:17 2015 +0200
tree 482d477dc139c712bec7f79212408c46e5e79409
parent ed2d72c1eb3643b7c109bdf387563d9b9a30c279

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>

arch/mips/kernel/traps.c

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index dbfa47c..4a0552d 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -761,6 +761,12 @@
 	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 @@
 
 		/*
 		 * 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 @@
 			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();
 		}