MIPS: KVM: Fix translation of MFC0 ErrCtl

The MIPS KVM dynamic translation is meant to translate "MFC0 rt, ErrCtl"
instructions into "ADD rt, zero, zero" to zero the destination register,
however the rt register number was copied into rt of the ADD instruction
encoding, which is the 2nd source operand. This results in "ADD zero,
zero, rt" which is a no-op, so only the first execution of each such
MFC0 from ErrCtl will actually read 0.

Fix the shift to put the rt from the MFC0 encoding into the rd field of
the ADD.

Fixes: 50c8308538dc ("KVM/MIPS32: Binary patching of select privileged instructions.")
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
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/mips/kvm/dyntrans.c b/arch/mips/kvm/dyntrans.c
index d4a86fb239cdf4b32f0109a63883d637cb0df60c..79b134c913336a77c613f3c9d37564a2641e715b 100644 (file)
--- a/arch/mips/kvm/dyntrans.c
+++ b/arch/mips/kvm/dyntrans.c
@@ -82,7 +82,7 @@ int kvm_mips_trans_mfc0(u32 inst, u32 *opc, struct kvm_vcpu *vcpu)
 
        if ((rd == MIPS_CP0_ERRCTL) && (sel == 0)) {
                mfc0_inst = CLEAR_TEMPLATE;
-               mfc0_inst |= ((rt & 0x1f) << 16);
+               mfc0_inst |= ((rt & 0x1f) << 11);
        } else {
                mfc0_inst = LW_TEMPLATE;
                mfc0_inst |= ((rt & 0x1f) << 16);