KVM: MIPS: Make ERET handle ERL before EXL

[ Upstream commit ede5f3e7b54a4347be4d8525269eae50902bd7cd ]

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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index 824be0da92cd3d46b9995c882fe69cdc32bcdf99..f49289f7fd2a048bd9337eb281bffe6922c3b9ee 100644 (file)
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -752,15 +752,15 @@ 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);