KVM: MIPS: Make ERET handle ERL before EXL

The ERET instruction to return from exception is used for returning from
exception level (Status.EXL) and error level (Status.ERL). If both bits
are set however we should be returning from ERL first, as ERL can
interrupt EXL, for example when an NMI is taken. KVM however checks EXL
first.

Fix the order of the checks to match the pseudocode in the instruction
set manual.

Fixes: e685c689f3a8 ("KVM/MIPS32: Privileged instruction/target branch emulation.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Cc: <stable@vger.kernel.org> # 3.10.x-
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index 8770f32c9e0bed601898dcbe3ac6504adaee8953..c45ef0f13dfa65a5c5c94981f166eb67db30aa2b 100644 (file)
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -790,15 +790,15 @@ enum emulation_result kvm_mips_emul_eret(struct kvm_vcpu *vcpu)
        struct mips_coproc *cop0 = vcpu->arch.cop0;
        enum emulation_result er = EMULATE_DONE;
 
-       if (kvm_read_c0_guest_status(cop0) & ST0_EXL) {
+       if (kvm_read_c0_guest_status(cop0) & ST0_ERL) {
+               kvm_clear_c0_guest_status(cop0, ST0_ERL);
+               vcpu->arch.pc = kvm_read_c0_guest_errorepc(cop0);
+       } else if (kvm_read_c0_guest_status(cop0) & ST0_EXL) {
                kvm_debug("[%#lx] ERET to %#lx\n", vcpu->arch.pc,
                          kvm_read_c0_guest_epc(cop0));
                kvm_clear_c0_guest_status(cop0, ST0_EXL);
                vcpu->arch.pc = kvm_read_c0_guest_epc(cop0);
 
-       } else if (kvm_read_c0_guest_status(cop0) & ST0_ERL) {
-               kvm_clear_c0_guest_status(cop0, ST0_ERL);
-               vcpu->arch.pc = kvm_read_c0_guest_errorepc(cop0);
        } else {
                kvm_err("[%#lx] ERET when MIPS_SR_EXL|MIPS_SR_ERL == 0\n",
                        vcpu->arch.pc);