KVM: MIPS: Implement HYPCALL emulation

Emulate the HYPCALL instruction added in the VZ ASE and used by the MIPS
paravirtualised guest support that is already merged. The new hypcall.c
handles arguments and the return value. No actual hypercalls are yet
supported, but this still allows us to safely step over hypercalls and
set an error code in the return value for forward compatibility.

Non-zero HYPCALL codes are not handled.

We also document the hypercall ABI which asm/kvm_para.h uses.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: David Daney <david.daney@cavium.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Cc: linux-doc@vger.kernel.org

4 files changed, 61 insertions, 0 deletions

diff --git a/arch/mips/kvm/Makefile b/arch/mips/kvm/Makefile
index 847429de780d..e56403c8a3f5 100644
--- a/arch/mips/kvm/Makefile
+++ b/arch/mips/kvm/Makefile
@@ -10,6 +10,7 @@ common-objs-$(CONFIG_CPU_HAS_MSA) += msa.o
 kvm-objs := $(common-objs-y) mips.o emulate.o entry.o \
 	    interrupt.o stats.o commpage.o \
 	    dyntrans.o trap_emul.o fpu.o
+kvm-objs += hypcall.o
 kvm-objs += mmu.o
 
 obj-$(CONFIG_KVM)	+= kvm.o
diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c
index d40cfaad4529..637753ea0a00 100644
--- a/arch/mips/kvm/emulate.c
+++ b/arch/mips/kvm/emulate.c
@@ -1143,6 +1143,9 @@ enum emulation_result kvm_mips_emulate_CP0(union mips_instruction inst,
 		case wait_op:
 			er = kvm_mips_emul_wait(vcpu);
 			break;
+		case hypcall_op:
+			er = kvm_mips_emul_hypcall(vcpu, inst);
+			break;
 		}
 	} else {
 		rt = inst.c0r_format.rt;
diff --git a/arch/mips/kvm/hypcall.c b/arch/mips/kvm/hypcall.c
new file mode 100644
index 000000000000..83063435195f
--- /dev/null
+++ b/arch/mips/kvm/hypcall.c
@@ -0,0 +1,53 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * KVM/MIPS: Hypercall handling.
+ *
+ * Copyright (C) 2015  Imagination Technologies Ltd.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kvm_host.h>
+#include <linux/kvm_para.h>
+
+#define MAX_HYPCALL_ARGS	4
+
+enum emulation_result kvm_mips_emul_hypcall(struct kvm_vcpu *vcpu,
+					    union mips_instruction inst)
+{
+	unsigned int code = (inst.co_format.code >> 5) & 0x3ff;
+
+	kvm_debug("[%#lx] HYPCALL %#03x\n", vcpu->arch.pc, code);
+
+	switch (code) {
+	case 0:
+		return EMULATE_HYPERCALL;
+	default:
+		return EMULATE_FAIL;
+	};
+}
+
+static int kvm_mips_hypercall(struct kvm_vcpu *vcpu, unsigned long num,
+			      const unsigned long *args, unsigned long *hret)
+{
+	/* Report unimplemented hypercall to guest */
+	*hret = -KVM_ENOSYS;
+	return RESUME_GUEST;
+}
+
+int kvm_mips_handle_hypcall(struct kvm_vcpu *vcpu)
+{
+	unsigned long num, args[MAX_HYPCALL_ARGS];
+
+	/* read hypcall number and arguments */
+	num = vcpu->arch.gprs[2];	/* v0 */
+	args[0] = vcpu->arch.gprs[4];	/* a0 */
+	args[1] = vcpu->arch.gprs[5];	/* a1 */
+	args[2] = vcpu->arch.gprs[6];	/* a2 */
+	args[3] = vcpu->arch.gprs[7];	/* a3 */
+
+	return kvm_mips_hypercall(vcpu, num,
+				  args, &vcpu->arch.gprs[2] /* v0 */);
+}
diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c
index b1fa53b252ea..3a854bb9e606 100644
--- a/arch/mips/kvm/trap_emul.c
+++ b/arch/mips/kvm/trap_emul.c
@@ -82,6 +82,10 @@ static int kvm_trap_emul_handle_cop_unusable(struct kvm_vcpu *vcpu)
 		ret = RESUME_HOST;
 		break;
 
+	case EMULATE_HYPERCALL:
+		ret = kvm_mips_handle_hypcall(vcpu);
+		break;
+
 	default:
 		BUG();
 	}