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
