From: Seth Forshee sforshee@digitalocean.com
[ Upstream commit 3e684903a8574ffc9475fdf13c4780a7adb506ad ]
A livepatch transition may stall indefinitely when a kvm vCPU is heavily loaded. To the host, the vCPU task is a user thread which is spending a very long time in the ioctl(KVM_RUN) syscall. During livepatch transition, set_notify_signal() will be called on such tasks to interrupt the syscall so that the task can be transitioned. This interrupts guest execution, but when xfer_to_guest_mode_work() sees that TIF_NOTIFY_SIGNAL is set but not TIF_SIGPENDING it concludes that an exit to user mode is unnecessary, and guest execution is resumed without transitioning the task for the livepatch.
This handling of TIF_NOTIFY_SIGNAL is incorrect, as set_notify_signal() is expected to break tasks out of interruptible kernel loops and cause them to return to userspace. Change xfer_to_guest_mode_work() to handle TIF_NOTIFY_SIGNAL the same as TIF_SIGPENDING, signaling to the vCPU run loop that an exit to userpsace is needed. Any pending task_work will be run when get_signal() is called from exit_to_user_mode_loop(), so there is no longer any need to run task work from xfer_to_guest_mode_work().
Suggested-by: "Eric W. Biederman" ebiederm@xmission.com Cc: Petr Mladek pmladek@suse.com Signed-off-by: Seth Forshee sforshee@digitalocean.com Message-Id: 20220504180840.2907296-1-sforshee@digitalocean.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/entry/kvm.c | 6 ------ 1 file changed, 6 deletions(-)
diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c index 9d09f489b60e..2e0f75bcb7fd 100644 --- a/kernel/entry/kvm.c +++ b/kernel/entry/kvm.c @@ -9,12 +9,6 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) int ret;
if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) { - clear_notify_signal(); - if (task_work_pending(current)) - task_work_run(); - } - - if (ti_work & _TIF_SIGPENDING) { kvm_handle_signal_exit(vcpu); return -EINTR; }