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>

2 files changed, 20 insertions, 1 deletions

diff --git a/arch/mips/kernel/mips-r2-to-r6-emul.c b/arch/mips/kernel/mips-r2-to-r6-emul.c
index f1d1b42d1902..6633fa97d431 100644
--- 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 dbfa47cdc8c1..4a0552dbcf4a 100644
--- 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();
                 }