This is a note to let you know that I've just added the patch titled entry/kvm: Exit to user mode when TIF_NOTIFY_SIGNAL is set to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: entry-kvm-exit-to-user-mode-when-tif_notify_signal-is-set.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 963feaebdd2ec09424d8d7dda014c4859cce19c5 Mon Sep 17 00:00:00 2001 From: Seth Forshee <sforshee@xxxxxxxxxxxxxxxx> Date: Wed, 4 May 2022 13:08:40 -0500 Subject: entry/kvm: Exit to user mode when TIF_NOTIFY_SIGNAL is set From: Seth Forshee <sforshee@xxxxxxxxxxxxxxxx> [ 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@xxxxxxxxxxxx> Cc: Petr Mladek <pmladek@xxxxxxxx> Signed-off-by: Seth Forshee <sforshee@xxxxxxxxxxxxxxxx> Message-Id: <20220504180840.2907296-1-sforshee@xxxxxxxxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/entry/kvm.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) --- a/kernel/entry/kvm.c +++ b/kernel/entry/kvm.c @@ -8,10 +8,7 @@ static int xfer_to_guest_mode_work(struc do { int ret; - if (ti_work & _TIF_NOTIFY_SIGNAL) - tracehook_notify_signal(); - - if (ti_work & _TIF_SIGPENDING) { + if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) { kvm_handle_signal_exit(vcpu); return -EINTR; } Patches currently in stable-queue which might be from sforshee@xxxxxxxxxxxxxxxx are queue-5.10/entry-kvm-exit-to-user-mode-when-tif_notify_signal-is-set.patch