Add usermem support for arm64 platform.

Signed-off-by: Haibo Xu <haibo.xu@arm.com>
PiperOrigin-RevId: 228249611
Change-Id: I1046e70bec4274f18b9948eefd6b0d546e4c48bb

pkg/sentry/usermem/BUILD

@@ -24,6 +24,7 @@ go_library(
         "bytes_io.go",
         "bytes_io_unsafe.go",
         "usermem.go",
+        "usermem_arm64.go",
         "usermem_x86.go",
     ],
     importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/usermem",

pkg/sentry/usermem/usermem_arm64.go

@@ -0,0 +1,53 @@
+// Copyright 2019 Google LLC
+//
+// 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 arm64
+
+package usermem
+
+import (
+	"encoding/binary"
+	"syscall"
+)
+
+const (
+	// PageSize is the system page size.
+	// arm64 support 4K/16K/64K page size,
+	// which can be get by syscall.Getpagesize().
+	// Currently, only 4K page size is supported.
+	PageSize = 1 << PageShift
+
+	// HugePageSize is the system huge page size.
+	HugePageSize = 1 << HugePageShift
+
+	// PageShift is the binary log of the system page size.
+	PageShift = 12
+
+	// HugePageShift is the binary log of the system huge page size.
+	// Should be calculated by "PageShift + (PageShift - 3)"
+	// when multiple page size support is ready.
+	HugePageShift = 21
+)
+
+var (
+	// ByteOrder is the native byte order (little endian).
+	ByteOrder = binary.LittleEndian
+)
+
+func init() {
+	// Make sure the page size is 4K on arm64 platform.
+	if size := syscall.Getpagesize(); size != PageSize {
+		panic("Only 4K page size is supported on arm64!")
+	}
+}