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, 45 insertions, 0 deletions

diff --git a/pkg/ring0/pagetables/pcids_aarch64.s b/pkg/ring0/pagetables/pcids_aarch64.s
new file mode 100644
index 000000000..e9d62d768
--- /dev/null
+++ b/pkg/ring0/pagetables/pcids_aarch64.s
@@ -0,0 +1,45 @@
+// 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
+
+#include "funcdata.h"
+#include "textflag.h"
+
+#define ID_AA64MMFR0_ASIDBITS_SHIFT 4
+#define ID_AA64MMFR0_ASIDBITS_16 2
+#define TCR_EL1_AS_BIT 36
+
+// GetASIDBits return the system ASID bits, 8 or 16 bits.
+//
+// func GetASIDBits() uint8
+TEXT ·GetASIDBits(SB),NOSPLIT,$0-1
+	// First, check whether 16bits ASID is supported.
+	// ID_AA64MMFR0_EL1.ASIDBITS[7:4] == 0010.
+	WORD $0xd5380700    // MRS ID_AA64MMFR0_EL1, R0
+	UBFX $ID_AA64MMFR0_ASIDBITS_SHIFT, R0, $4, R0
+	CMPW $ID_AA64MMFR0_ASIDBITS_16, R0
+	BNE bits_8
+
+	// Second, check whether 16bits ASID is enabled.
+	// TCR_EL1.AS[36] == 1.
+	WORD $0xd5382040    // MRS TCR_EL1, R0
+	TBZ  $TCR_EL1_AS_BIT, R0, bits_8
+	MOVD $16, R0
+	B done
+bits_8:
+	MOVD $8, R0
+done:
+	MOVB R0, ret+0(FP)
+	RET