MIPS: KVM: Add FP exception handling

Add guest exception handling for floating point exceptions and
coprocessor 1 unusable exceptions.

Floating point exceptions from the guest need passing to the guest
kernel, so for these a guest FPE is emulated.

Also, coprocessor 1 unusable exceptions are normally passed straight
through to the guest (because no guest FPU was supported), but the
hypervisor can now handle them if the guest has its FPU enabled by
restoring the guest FPU context and enabling the FPU.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

1 files changed, 36 insertions, 3 deletions

diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c
index 408af244aed2..421d5b815f24 100644
--- a/arch/mips/kvm/trap_emul.c
+++ b/arch/mips/kvm/trap_emul.c
@@ -39,16 +39,30 @@ static gpa_t kvm_trap_emul_gva_to_gpa_cb(gva_t gva)
 
 static int kvm_trap_emul_handle_cop_unusable(struct kvm_vcpu *vcpu)
 {
+        struct mips_coproc *cop0 = vcpu->arch.cop0;
         struct kvm_run *run = vcpu->run;
         uint32_t __user *opc = (uint32_t __user *) vcpu->arch.pc;
         unsigned long cause = vcpu->arch.host_cp0_cause;
         enum emulation_result er = EMULATE_DONE;
         int ret = RESUME_GUEST;
 
-        if (((cause & CAUSEF_CE) >> CAUSEB_CE) == 1)
-                er = kvm_mips_emulate_fpu_exc(cause, opc, run, vcpu);
-        else
+        if (((cause & CAUSEF_CE) >> CAUSEB_CE) == 1) {
+                /* FPU Unusable */
+                if (!kvm_mips_guest_has_fpu(&vcpu->arch) ||
+                    (kvm_read_c0_guest_status(cop0) & ST0_CU1) == 0) {
+                        /*
+                         * Unusable/no FPU in guest:
+                         * deliver guest COP1 Unusable Exception
+                         */
+                        er = kvm_mips_emulate_fpu_exc(cause, opc, run, vcpu);
+                } else {
+                        /* Restore FPU state */
+                        kvm_own_fpu(vcpu);
+                        er = EMULATE_DONE;
+                }
+        } else {
                 er = kvm_mips_emulate_inst(cause, opc, run, vcpu);
+        }
 
         switch (er) {
         case EMULATE_DONE:
@@ -348,6 +362,24 @@ static int kvm_trap_emul_handle_trap(struct kvm_vcpu *vcpu)
         return ret;
 }
 
+static int kvm_trap_emul_handle_fpe(struct kvm_vcpu *vcpu)
+{
+        struct kvm_run *run = vcpu->run;
+        uint32_t __user *opc = (uint32_t __user *)vcpu->arch.pc;
+        unsigned long cause = vcpu->arch.host_cp0_cause;
+        enum emulation_result er = EMULATE_DONE;
+        int ret = RESUME_GUEST;
+
+        er = kvm_mips_emulate_fpe_exc(cause, opc, run, vcpu);
+        if (er == EMULATE_DONE) {
+                ret = RESUME_GUEST;
+        } else {
+                run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+                ret = RESUME_HOST;
+        }
+        return ret;
+}
+
 static int kvm_trap_emul_handle_msa_disabled(struct kvm_vcpu *vcpu)
 {
         struct kvm_run *run = vcpu->run;
@@ -576,6 +608,7 @@ static struct kvm_mips_callbacks kvm_trap_emul_callbacks = {
         .handle_res_inst = kvm_trap_emul_handle_res_inst,
         .handle_break = kvm_trap_emul_handle_break,
         .handle_trap = kvm_trap_emul_handle_trap,
+        .handle_fpe = kvm_trap_emul_handle_fpe,
         .handle_msa_disabled = kvm_trap_emul_handle_msa_disabled,
 
         .vm_init = kvm_trap_emul_vm_init,