gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/sentry/hostmm/membarrier.go (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package hostmm
    16  
    17  import (
    18  	"golang.org/x/sys/unix"
    19  	"gvisor.dev/gvisor/pkg/abi/linux"
    20  	"gvisor.dev/gvisor/pkg/log"
    21  )
    22  
    23  var (
    24  	haveMembarrierGlobal           = false
    25  	haveMembarrierPrivateExpedited = false
    26  )
    27  
    28  func init() {
    29  	supported, _, e := unix.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_QUERY, 0 /* flags */, 0 /* unused */)
    30  	if e != 0 {
    31  		if e != unix.ENOSYS {
    32  			log.Warningf("membarrier(MEMBARRIER_CMD_QUERY) failed: %s", e.Error())
    33  		}
    34  		return
    35  	}
    36  	// We don't use MEMBARRIER_CMD_GLOBAL_EXPEDITED because this sends IPIs to
    37  	// all CPUs running tasks that have previously invoked
    38  	// MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED, which presents a DOS risk.
    39  	// (MEMBARRIER_CMD_GLOBAL is synchronize_rcu(), i.e. it waits for an RCU
    40  	// grace period to elapse without bothering other CPUs.
    41  	// MEMBARRIER_CMD_PRIVATE_EXPEDITED sends IPIs only to CPUs running tasks
    42  	// sharing the caller's MM.)
    43  	if supported&linux.MEMBARRIER_CMD_GLOBAL != 0 {
    44  		haveMembarrierGlobal = true
    45  	}
    46  	if req := uintptr(linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED | linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED); supported&req == req {
    47  		if _, _, e := unix.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
    48  			log.Warningf("membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED) failed: %s", e.Error())
    49  		} else {
    50  			haveMembarrierPrivateExpedited = true
    51  		}
    52  	}
    53  }
    54  
    55  // HaveGlobalMemoryBarrier returns true if GlobalMemoryBarrier is supported.
    56  func HaveGlobalMemoryBarrier() bool {
    57  	return haveMembarrierGlobal
    58  }
    59  
    60  // GlobalMemoryBarrier blocks until "all running threads [in the host OS] have
    61  // passed through a state where all memory accesses to user-space addresses
    62  // match program order between entry to and return from [GlobalMemoryBarrier]",
    63  // as for membarrier(2).
    64  //
    65  // Preconditions: HaveGlobalMemoryBarrier() == true.
    66  func GlobalMemoryBarrier() error {
    67  	if _, _, e := unix.Syscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_GLOBAL, 0 /* flags */, 0 /* unused */); e != 0 {
    68  		return e
    69  	}
    70  	return nil
    71  }
    72  
    73  // HaveProcessMemoryBarrier returns true if ProcessMemoryBarrier is supported.
    74  func HaveProcessMemoryBarrier() bool {
    75  	return haveMembarrierPrivateExpedited
    76  }
    77  
    78  // ProcessMemoryBarrier is equivalent to GlobalMemoryBarrier, but only
    79  // synchronizes with threads sharing a virtual address space (from the host OS'
    80  // perspective) with the calling thread.
    81  //
    82  // Preconditions: HaveProcessMemoryBarrier() == true.
    83  func ProcessMemoryBarrier() error {
    84  	if _, _, e := unix.RawSyscall(unix.SYS_MEMBARRIER, linux.MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0 /* flags */, 0 /* unused */); e != 0 {
    85  		return e
    86  	}
    87  	return nil
    88  }