mirror of
https://github.com/torvalds/linux.git
synced 2025-10-31 08:38:45 +02:00
3e684903a8
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>
49 lines
1.1 KiB
C
49 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
|
|
#include <linux/entry-kvm.h>
|
|
#include <linux/kvm_host.h>
|
|
|
|
static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
|
|
{
|
|
do {
|
|
int ret;
|
|
|
|
if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
|
|
kvm_handle_signal_exit(vcpu);
|
|
return -EINTR;
|
|
}
|
|
|
|
if (ti_work & _TIF_NEED_RESCHED)
|
|
schedule();
|
|
|
|
if (ti_work & _TIF_NOTIFY_RESUME)
|
|
resume_user_mode_work(NULL);
|
|
|
|
ret = arch_xfer_to_guest_mode_handle_work(vcpu, ti_work);
|
|
if (ret)
|
|
return ret;
|
|
|
|
ti_work = read_thread_flags();
|
|
} while (ti_work & XFER_TO_GUEST_MODE_WORK || need_resched());
|
|
return 0;
|
|
}
|
|
|
|
int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu)
|
|
{
|
|
unsigned long ti_work;
|
|
|
|
/*
|
|
* This is invoked from the outer guest loop with interrupts and
|
|
* preemption enabled.
|
|
*
|
|
* KVM invokes xfer_to_guest_mode_work_pending() with interrupts
|
|
* disabled in the inner loop before going into guest mode. No need
|
|
* to disable interrupts here.
|
|
*/
|
|
ti_work = read_thread_flags();
|
|
if (!(ti_work & XFER_TO_GUEST_MODE_WORK))
|
|
return 0;
|
|
|
|
return xfer_to_guest_mode_work(vcpu, ti_work);
|
|
}
|
|
EXPORT_SYMBOL_GPL(xfer_to_guest_mode_handle_work);
|