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Fix race between un-pausing vcpu and requesting vcpu pause

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To ensure that we do not miss pause request sent while we were in paused
state, or were exiting paused state, let's start using
KVM_SET_SIGNAL_MASK. SIGRTMIN() + 0 signal will be blocked and thus is
not delivered, and it will only be checked when KVM_RUN is being
executed, reliably interrupting KVM_RUN.

TEST=cargo test --features plugin; cargo test -p kvm; ./build_test
BUG=chromium:800626

Change-Id: Iae67a411c23c2b14fbfcbc7d53d0bc86ec4b67d9
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/944850
Reviewed-by: Zach Reizner <zachr@chromium.org>
This commit is contained in:
Dmitry Torokhov 2018-02-21 10:21:56 -08:00 committed by chrome-bot
parent e423460238
commit 532a94c1c8
2 changed files with 32 additions and 1 deletions
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18
src/plugin/mod.rs
View file

@ -26,7 +26,7 @@ use io_jail::{self, Minijail};
use kvm::{Kvm, Vm, Vcpu, VcpuExit, IoeventAddress, NoDatamatch};
use sys_util::{EventFd, MmapError, Killable, SignalFd, SignalFdError, Poller, Pollable,
GuestMemory, Result as SysResult, Error as SysError,
register_signal_handler, SIGRTMIN,
register_signal_handler, block_signal, clear_signal, SIGRTMIN,
geteuid, getegid};
use Config;
@ -307,10 +307,21 @@ pub fn run_vcpus(kvm: &Kvm,
unsafe {
extern "C" fn handle_signal() {}
// Our signal handler does nothing and is trivially async signal safe.
// We need to install this signal handler even though we do block
// the signal below, to ensure that this signal will interrupt
// execution of KVM_RUN (this is implementation issue).
register_signal_handler(SIGRTMIN() + 0, handle_signal)
.expect("failed to register vcpu signal handler");
}
// We do not really want the signal handler to run...
block_signal(SIGRTMIN() + 0)
.expect("failed to block signal");
// Tell KVM to not block anything when entering kvm run
// because we will be using first RT signal to kick the VCPU.
vcpu.set_signal_mask(&[])
.expect("failed to set up KVM VCPU signal mask");
let res = vcpu_plugin.init(&vcpu);
vcpu_thread_barrier.wait();
if let Err(e) = res {
@ -356,6 +367,11 @@ pub fn run_vcpus(kvm: &Kvm,
break;
}
// Try to clear the signal that we use to kick VCPU if it is
// pending before attempting to handle pause requests.
clear_signal(SIGRTMIN() + 0)
.expect("failed to clear pending signal");
if let Err(e) = vcpu_plugin.pre_run(&vcpu) {
error!("failed to process pause on vcpu {}: {:?}", cpu_id, e);
break;

15
tests/plugin_vcpu_pause.c
View file

@ -238,6 +238,21 @@ int main(int argc, char** argv) {
return 1;
}
signal_unpause(crosvm, false);
/* Wait until VCPU thread tells us that it is no longer paused */
read(g_kill_evt, &dummy, sizeof(dummy));
/*
* Try pausing VCPUs 3rd time to see if we will miss pause
* request as we are exiting previous pause.
*/
ret = signal_pause(crosvm);
if (ret) {
fprintf(stderr, "failed to pause vcpus (2nd time): %d\n", ret);
return 1;
}
signal_unpause(crosvm, true);
/* Wait until VCPU thread tells us that it is no longer paused */