KVM: MIPS: Make ERET handle ERL before EXL

commit ede5f3e7b54a4347be4d8525269eae50902bd7cd upstream.

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 KrÄ\8dmáÅ\99" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index 4cfb5bddaa9bcbba1773b9f413d7e9feb21e6de9..716285497e0e02ce6380767a4e7a774e22d53799 100644 (file)
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -254,15 +254,15 @@ 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 {
                printk("[%#lx] ERET when MIPS_SR_EXL|MIPS_SR_ERL == 0\n",
                       vcpu->arch.pc);