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Message-Id: <20220614021116.1101331-5-sashal@kernel.org>
Date: Mon, 13 Jun 2022 22:11:14 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: Seth Forshee <sforshee@...italocean.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Petr Mladek <pmladek@...e.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Sasha Levin <sashal@...nel.org>, tglx@...utronix.de,
peterz@...radead.org, luto@...nel.org
Subject: [PATCH MANUALSEL 5.18 5/6] entry/kvm: Exit to user mode when TIF_NOTIFY_SIGNAL is set
From: Seth Forshee <sforshee@...italocean.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@...ssion.com>
Cc: Petr Mladek <pmladek@...e.com>
Signed-off-by: Seth Forshee <sforshee@...italocean.com>
Message-Id: <20220504180840.2907296-1-sforshee@...italocean.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.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;
}
--
2.35.1
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