On Tue, 27 Feb 2024 11:49:21 +0000
David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote:
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index c16b6d394d55..d8b5326ecebc 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -1736,9 +1736,23 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port)
> unsigned long flags;
> int rc = -EWOULDBLOCK;
>
> - read_lock_irqsave(&gpc->lock, flags);
> + local_irq_save(flags);
> + if (!read_trylock(&gpc->lock)) {
Note, directly disabling interrupts in PREEMPT_RT is just as bad as doing
so in non RT and the taking a mutex.
Worse yet, in PREEMPT_RT read_unlock_irqrestore() isn't going to re-enable
interrupts.
Not really sure what the best solution is here.
-- Steve
> + /*
> + * When PREEMPT_RT turns locks into mutexes, rwlocks are
> + * turned into mutexes and most interrupts are threaded.
> + * But timer events may be delivered in hardirq mode due
> + * to using HRTIMER_MODE_ABS_HARD. So bail to the slow
> + * path if the trylock fails in interrupt context.
> + */
> + if (in_interrupt())
> + goto out;
> +
> + read_lock(&gpc->lock);
> + }
> +
> if (!kvm_gpc_check(gpc, PAGE_SIZE))
> - goto out;
> + goto out_unlock;
>
> if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) {
> struct shared_info *shinfo = gpc->khva;
