Split the kvm ut test cases to correspond to different platforms

Split the kvm ut test cases to pass unit-tests on Arm64.
    I will add the tls and full-context test cases for Arm64 later.

Signed-off-by: Bin Lu <bin.lu@arm.com>

pkg/sentry/platform/kvm/BUILD

@@ -60,6 +60,7 @@ go_library(
 go_test(
     name = "kvm_test",
     srcs = [
+        "kvm_amd64_test.go",
         "kvm_test.go",
         "virtual_map_test.go",
     ],

pkg/sentry/platform/kvm/kvm_amd64_test.go

@@ -0,0 +1,51 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build amd64
+
+package kvm
+
+import (
+	"testing"
+
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/platform"
+	"gvisor.dev/gvisor/pkg/sentry/platform/kvm/testutil"
+	"gvisor.dev/gvisor/pkg/sentry/platform/ring0"
+	"gvisor.dev/gvisor/pkg/sentry/platform/ring0/pagetables"
+)
+
+func TestSegments(t *testing.T) {
+	applicationTest(t, true, testutil.TwiddleSegments, func(c *vCPU, regs *arch.Registers, pt *pagetables.PageTables) bool {
+		testutil.SetTestSegments(regs)
+		for {
+			var si arch.SignalInfo
+			if _, err := c.SwitchToUser(ring0.SwitchOpts{
+				Registers:          regs,
+				FloatingPointState: dummyFPState,
+				PageTables:         pt,
+				FullRestore:        true,
+			}, &si); err == platform.ErrContextInterrupt {
+				continue // Retry.
+			} else if err != nil {
+				t.Errorf("application segment check with full restore got unexpected error: %v", err)
+			}
+			if err := testutil.CheckTestSegments(regs); err != nil {
+				t.Errorf("application segment check with full restore failed: %v", err)
+			}
+			break // Done.
+		}
+		return false
+	})
+}

pkg/sentry/platform/kvm/kvm_test.go

@@ -262,30 +262,6 @@ func TestRegistersFault(t *testing.T) {
 	})
 }
 
-func TestSegments(t *testing.T) {
-	applicationTest(t, true, testutil.TwiddleSegments, func(c *vCPU, regs *arch.Registers, pt *pagetables.PageTables) bool {
-		testutil.SetTestSegments(regs)
-		for {
-			var si arch.SignalInfo
-			if _, err := c.SwitchToUser(ring0.SwitchOpts{
-				Registers:          regs,
-				FloatingPointState: dummyFPState,
-				PageTables:         pt,
-				FullRestore:        true,
-			}, &si); err == platform.ErrContextInterrupt {
-				continue // Retry.
-			} else if err != nil {
-				t.Errorf("application segment check with full restore got unexpected error: %v", err)
-			}
-			if err := testutil.CheckTestSegments(regs); err != nil {
-				t.Errorf("application segment check with full restore failed: %v", err)
-			}
-			break // Done.
-		}
-		return false
-	})
-}
-
 func TestBounce(t *testing.T) {
 	applicationTest(t, true, testutil.SpinLoop, func(c *vCPU, regs *arch.Registers, pt *pagetables.PageTables) bool {
 		go func() {

pkg/sentry/platform/kvm/testutil/testutil_arm64.s

@@ -104,3 +104,9 @@ TEXT ·TwiddleRegsSyscall(SB),NOSPLIT,$0
 	TWIDDLE_REGS()
 	SVC
 	RET // never reached
+
+TEXT ·TwiddleRegsFault(SB),NOSPLIT,$0
+        TWIDDLE_REGS()
+        // Branch to Register branches unconditionally to an address in <Rn>.
+        JMP (R4) // <=> br x4, must fault
+        RET // never reached