linux-kernel - Re: [PATCH 2/5] KVM: Bail from the dirty ring reset flow if a signal is pending

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Message-ID: <Z4TdaxQwMuA7NM5g@yzhao56-desk.sh.intel.com>
Date: Mon, 13 Jan 2025 17:31:23 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Paolo Bonzini <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Peter Xu <peterx@...hat.com>, Maxim Levitsky
	<mlevitsk@...hat.com>
Subject: Re: [PATCH 2/5] KVM: Bail from the dirty ring reset flow if a signal
 is pending

On Fri, Jan 10, 2025 at 05:04:06PM -0800, Sean Christopherson wrote:
> Abort a dirty ring reset if the current task has a pending signal, as the
> hard limit of INT_MAX entries doesn't ensure KVM will respond to a signal
> in a timely fashion.
> 
> Fixes: fb04a1eddb1a ("KVM: X86: Implement ring-based dirty memory tracking")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  virt/kvm/dirty_ring.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
> index 2faf894dec5a..a81ad17d5eef 100644
> --- a/virt/kvm/dirty_ring.c
> +++ b/virt/kvm/dirty_ring.c
> @@ -117,6 +117,9 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
>  	cur_slot = cur_offset = mask = 0;
>  
>  	while (likely((*nr_entries_reset) < INT_MAX)) {
> +		if (signal_pending(current))
> +			return -EINTR;
Will it break the userspace when a signal is pending? e.g. QEMU might report an
error like
"kvm_dirty_ring_reap_locked: Assertion `ret == total' failed".

>  		entry = &ring->dirty_gfns[ring->reset_index & (ring->size - 1)];
>  
>  		if (!kvm_dirty_gfn_harvested(entry))
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
>