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// 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.
package hostmm
import (
"syscall"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/log"
)
var (
haveMembarrierGlobal = false
haveMembarrierPrivateExpedited = false
)
func init() {
supported, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_QUERY, 0 /* flags */, 0 /* unused */)
if e != 0 {
if e != syscall.ENOSYS {
log.Warningf("membarrier(MEMBARRIER_CMD_QUERY) failed: %s", e.Error())
}
return
}
// We don't use MEMBARRIER_CMD_GLOBAL_EXPEDITED because this sends IPIs to
// all CPUs running tasks that have previously invoked
// MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, which presents a DOS risk.
// (MEMBARRIER_CMD_GLOBAL is synchronize_rcu(), i.e. it waits for an RCU
// grace period to elapse without bothering other CPUs.
// MEMBARRIER_CMD_PRIVATE_EXPEDITED sends IPIs only to CPUs running tasks
// sharing the caller's MM.)
if supported&linux.MEMBARRIER_CMD_GLOBAL != 0 {
haveMembarrierGlobal = true
}
if req := uintptr(linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED | linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED); supported&req == req {
if _, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
log.Warningf("membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED) failed: %s", e.Error())
} else {
haveMembarrierPrivateExpedited = true
}
}
}
// HaveGlobalMemoryBarrier returns true if GlobalMemoryBarrier is supported.
func HaveGlobalMemoryBarrier() bool {
return haveMembarrierGlobal
}
// GlobalMemoryBarrier blocks until "all running threads [in the host OS] have
// passed through a state where all memory accesses to user-space addresses
// match program order between entry to and return from [GlobalMemoryBarrier]",
// as for membarrier(2).
//
// Preconditions: HaveGlobalMemoryBarrier() == true.
func GlobalMemoryBarrier() error {
if _, _, e := syscall.Syscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_GLOBAL, 0 /* flags */, 0 /* unused */); e != 0 {
return e
}
return nil
}
// HaveProcessMemoryBarrier returns true if ProcessMemoryBarrier is supported.
func HaveProcessMemoryBarrier() bool {
return haveMembarrierPrivateExpedited
}
// ProcessMemoryBarrier is equivalent to GlobalMemoryBarrier, but only
// synchronizes with threads sharing a virtual address space (from the host OS'
// perspective) with the calling thread.
//
// Preconditions: HaveProcessMemoryBarrier() == true.
func ProcessMemoryBarrier() error {
if _, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
return e
}
return nil
}
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