Move ring0 package.

This allows the package to serve as a general purpose ring0 support package, as
opposed to being bound to specific sentry platforms.

Updates #5039

PiperOrigin-RevId: 355220044

1 files changed, 32 insertions, 0 deletions

diff --git a/pkg/ring0/pagetables/pcids_aarch64.go b/pkg/ring0/pagetables/pcids_aarch64.go
new file mode 100644
index 000000000..fbfd41d83
--- /dev/null
+++ b/pkg/ring0/pagetables/pcids_aarch64.go
@@ -0,0 +1,32 @@
+// 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 arm64
+
+package pagetables
+
+// limitPCID is the maximum value of PCIDs.
+//
+// In VMSAv8-64, the PCID(ASID) size is an IMPLEMENTATION DEFINED choice
+// of 8 bits or 16 bits, and ID_AA64MMFR0_EL1.ASIDBits identifies the
+// supported size. When an implementation supports a 16-bit ASID, TCR_ELx.AS
+// selects whether the top 8 bits of the ASID are used.
+var limitPCID uint16
+
+// GetASIDBits return the system ASID bits, 8 or 16 bits.
+func GetASIDBits() uint8
+
+func init() {
+	limitPCID = uint16(1)<<GetASIDBits() - 1
+}