Re: [PATCH v2 1/1] KVM: powerpc: Use generic xfer to guest work function

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Early return on pending signals bypasses the vCPU exit tracepoint
--

commit 902f7514807a6e7be76bed1f71c7055f873978b8
Author: Vishal Chourasia <vishalc@linux.ibm.com>

KVM: powerpc: Use generic xfer to guest work function

This commit replaces open-coded need_resched() and cond_resched() checks
with the generic xfer_to_guest_mode_handle_work() infrastructure in powerpc
KVM run loops to properly handle deferred task work like CFS bandwidth
throttling.

> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 61dbeea317f3b..a1b2077561bb5 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c

[ ... ]

> @@ -4899,8 +4923,21 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
>  		}
>  	}
>  
> -	if (need_resched())
> -		cond_resched();
> +	/*
> +	 * Run pending work before (re-)entering the guest, most importantly
> +	 * task_work queued via TWA_RESUME (e.g. the deferred CFS bandwidth
> +	 * throttle, which only sets TIF_NOTIFY_RESUME). Without this a CPU-bound
> +	 * vCPU that keeps returning RESUME_GUEST never reaches an exit-to-user
> +	 * point, so the throttle is never enforced and the task runs far beyond
> +	 * its quota. The helper also handles reschedule and signals, replacing
> +	 * the cond_resched() that was here. It may schedule(), so it runs before
> +	 * preemption and IRQs are disabled, with no vcore/KVM locks held. This
> +	 * is the per-reentry site shared by the bare-metal and pseries (nested)
> +	 * paths, so both are covered.
> +	 */
> +	r = kvm_xfer_to_guest_mode_handle_work(vcpu);
> +	if (r)	/* -EINTR: signal pending, exit to userspace (KVM_EXIT_INTR) */
> +		return r;

[Severity: Medium]
When kvm_xfer_to_guest_mode_handle_work() returns a pending signal, this
direct return bypasses the done: label at the end of the function.

Since trace_kvmppc_run_vcpu_enter() is executed unconditionally at the start
of kvmhv_run_single_vcpu(), does this early return cause unbalanced
tracepoints on signal-driven userspace exits? This might break performance
monitoring tools that rely on symmetric enter/exit events.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260701183030.3610451-2-vishalc@linux.ibm.com?part=1