linux-kernel - Re: [PATCH v3 6/6] KVM: Assert that slots_lock is held when resetting per-vCPU dirty rings

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Message-ID: <0edbcc4a-4cf6-4836-a573-dadec93f6f66@linux.intel.com>
Date: Tue, 20 May 2025 15:04:16 +0800
From: Binbin Wu <binbin.wu@...ux.intel.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>,
 Yan Zhao <yan.y.zhao@...el.com>, Maxim Levitsky <mlevitsk@...hat.com>,
 James Houghton <jthoughton@...gle.com>, Pankaj Gupta <pankaj.gupta@....com>
Subject: Re: [PATCH v3 6/6] KVM: Assert that slots_lock is held when resetting
 per-vCPU dirty rings



On 5/17/2025 5:35 AM, Sean Christopherson wrote:
> Assert that slots_lock is held in kvm_dirty_ring_reset() and add a comment
> to explain _why_ slots needs to be held for the duration of the reset.
>
> Link: https://lore.kernel.org/all/aCSns6Q5oTkdXUEe@google.com
> Suggested-by: James Houghton <jthoughton@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   virt/kvm/dirty_ring.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/virt/kvm/dirty_ring.c b/virt/kvm/dirty_ring.c
> index 54734025658a..1ba02a06378c 100644
> --- a/virt/kvm/dirty_ring.c
> +++ b/virt/kvm/dirty_ring.c
> @@ -122,6 +122,14 @@ int kvm_dirty_ring_reset(struct kvm *kvm, struct kvm_dirty_ring *ring,
>   	unsigned long mask = 0;
>   	struct kvm_dirty_gfn *entry;
>   
> +	/*
> +	 * Ensure concurrent calls to KVM_RESET_DIRTY_RINGS are serialized,
> +	 * e.g. so that KVM fully resets all entries processed by a given call
It seems that "e.g." is not needed?

> +	 * before returning to userspace.  Holding slots_lock also protects
> +	 * the various memslot accesses.
> +	 */
> +	lockdep_assert_held(&kvm->slots_lock);
> +
>   	while (likely((*nr_entries_reset) < INT_MAX)) {
>   		if (signal_pending(current))
>   			return -EINTR;