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Commit 443c4403 authored by Maciej W. Rozycki's avatar Maciej W. Rozycki Committed by Ralf Baechle
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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: default avatarMaciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9704/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent ed2d72c1

arch/mips/kernel/mips-r2-to-r6-emul.c

+6 −0
Original line number Diff line number Diff line
@@ -1169,6 +1169,12 @@ int mipsr2_decoder(struct pt_regs *regs, u32 inst) 
		err = 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;



		/*

		 * this is a tricky issue - lose_fpu() uses LL/SC atomics

		 * if FPU is owned and effectively cancels user level LL/SC.

arch/mips/kernel/traps.c

+14 −1
Original line number Diff line number Diff line
@@ -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();

		}