91 lines
3.2 KiB
Go
91 lines
3.2 KiB
Go
// Copyright 2020 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package hostmm
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import (
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"syscall"
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"golang.org/x/sys/unix"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/log"
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)
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var (
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haveMembarrierGlobal = false
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haveMembarrierPrivateExpedited = false
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)
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func init() {
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supported, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_QUERY, 0 /* flags */, 0 /* unused */)
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if e != 0 {
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if e != syscall.ENOSYS {
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log.Warningf("membarrier(MEMBARRIER_CMD_QUERY) failed: %s", e.Error())
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}
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return
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}
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// We don't use MEMBARRIER_CMD_GLOBAL_EXPEDITED because this sends IPIs to
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// all CPUs running tasks that have previously invoked
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// MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, which presents a DOS risk.
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// (MEMBARRIER_CMD_GLOBAL is synchronize_rcu(), i.e. it waits for an RCU
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// grace period to elapse without bothering other CPUs.
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// MEMBARRIER_CMD_PRIVATE_EXPEDITED sends IPIs only to CPUs running tasks
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// sharing the caller's MM.)
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if supported&linux.MEMBARRIER_CMD_GLOBAL != 0 {
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haveMembarrierGlobal = true
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}
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if req := uintptr(linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED | linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED); supported&req == req {
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if _, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
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log.Warningf("membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED) failed: %s", e.Error())
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} else {
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haveMembarrierPrivateExpedited = true
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}
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}
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}
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// HaveGlobalMemoryBarrier returns true if GlobalMemoryBarrier is supported.
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func HaveGlobalMemoryBarrier() bool {
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return haveMembarrierGlobal
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}
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// GlobalMemoryBarrier blocks until "all running threads [in the host OS] have
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// passed through a state where all memory accesses to user-space addresses
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// match program order between entry to and return from [GlobalMemoryBarrier]",
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// as for membarrier(2).
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//
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// Preconditions: HaveGlobalMemoryBarrier() == true.
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func GlobalMemoryBarrier() error {
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if _, _, e := syscall.Syscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_GLOBAL, 0 /* flags */, 0 /* unused */); e != 0 {
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return e
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}
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return nil
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}
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// HaveProcessMemoryBarrier returns true if ProcessMemoryBarrier is supported.
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func HaveProcessMemoryBarrier() bool {
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return haveMembarrierPrivateExpedited
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}
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// ProcessMemoryBarrier is equivalent to GlobalMemoryBarrier, but only
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// synchronizes with threads sharing a virtual address space (from the host OS'
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// perspective) with the calling thread.
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//
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// Preconditions: HaveProcessMemoryBarrier() == true.
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func ProcessMemoryBarrier() error {
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if _, _, e := syscall.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
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return e
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}
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return nil
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}
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