Move pagetables.limitPCID to arch-specific file.

X86 provide 12 bits for PCID while arm64 support
8/16 bits ASID.

Signed-off-by: Haibo Xu <haibo.xu@arm.com>
Change-Id: I0bd9236e44e6b6c4c88eb6e9adc5ac27b918bf6c

5 files changed, 101 insertions, 4 deletions

diff --git a/pkg/sentry/platform/ring0/pagetables/BUILD b/pkg/sentry/platform/ring0/pagetables/BUILD
index 581841555..16d5f478b 100644
--- a/pkg/sentry/platform/ring0/pagetables/BUILD
+++ b/pkg/sentry/platform/ring0/pagetables/BUILD
@@ -81,6 +81,9 @@ go_library(
         "pagetables_arm64.go",
         "pagetables_x86.go",
         "pcids.go",
+        "pcids_aarch64.go",
+        "pcids_aarch64.s",
+        "pcids_x86.go",
         "walker_amd64.go",
         "walker_arm64.go",
         "walker_empty.go",
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids.go b/pkg/sentry/platform/ring0/pagetables/pcids.go
index 9206030bf..964496aac 100644
--- a/pkg/sentry/platform/ring0/pagetables/pcids.go
+++ b/pkg/sentry/platform/ring0/pagetables/pcids.go
@@ -18,9 +18,6 @@ import (
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
-// limitPCID is the number of valid PCIDs.
-const limitPCID = 4096
-
 // PCIDs is a simple PCID database.
 //
 // This is not protected by locks and is thus suitable for use only with a
@@ -44,7 +41,7 @@ type PCIDs struct {
 //
 // Nil is returned iff the start and size are out of range.
 func NewPCIDs(start, size uint16) *PCIDs {
-	if start+uint16(size) >= limitPCID {
+	if start+uint16(size) > limitPCID {
 		return nil // See comment.
 	}
 	p := &PCIDs{
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.go b/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.go
new file mode 100644
index 000000000..fbfd41d83
--- /dev/null
+++ b/pkg/sentry/platform/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
+}
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.s b/pkg/sentry/platform/ring0/pagetables/pcids_aarch64.s
new file mode 100644
index 000000000..e9d62d768
--- /dev/null
+++ b/pkg/sentry/platform/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
diff --git a/pkg/sentry/platform/ring0/pagetables/pcids_x86.go b/pkg/sentry/platform/ring0/pagetables/pcids_x86.go
new file mode 100644
index 000000000..91fc5e8dd
--- /dev/null
+++ b/pkg/sentry/platform/ring0/pagetables/pcids_x86.go
@@ -0,0 +1,20 @@
+// 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 i386 amd64
+
+package pagetables
+
+// limitPCID is the maximum value of valid PCIDs.
+const limitPCID = 4095