[PATCH 3.16 097/254] MIPS: Always clear FCSR cause bits after emulation

Ben Hutchings
2018-02-28T16:15:16Z

From: "Maciej W. Rozycki" <macro@linux-mips.org>

commit 443c44032a54f9acf027a8e688380fddc809bc19 upstream.

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>
[bwh: Backported to 3.16: drop changes in mips-r2-to-r6-emul and simulate_fp()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -775,7 +775,7 @@ asmlinkage void do_fpe(struct pt_regs *r

/*
* 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;

@@ -1292,6 +1292,13 @@ asmlinkage void do_cpu(struct pt_regs *r
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();
}