linux-kernel - Re: [PATCH v2 25/27] KVM: x86/mmu: Drop @slot param from exported/external page-track APIs

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Date:   Fri, 17 Mar 2023 16:28:56 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>, <kvm@...r.kernel.org>,
        <intel-gfx@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Ben Gardon <bgardon@...gle.com>,
        <intel-gvt-dev@...ts.freedesktop.org>
Subject: Re: [PATCH v2 25/27] KVM: x86/mmu: Drop @slot param from
 exported/external page-track APIs

On Fri, Mar 10, 2023 at 04:22:56PM -0800, Sean Christopherson wrote:
...
> +int kvm_write_track_add_gfn(struct kvm *kvm, gfn_t gfn)
> +{
> +	struct kvm_memory_slot *slot;
> +	int idx;
> +
> +	idx = srcu_read_lock(&kvm->srcu);
> +
> +	slot = gfn_to_memslot(kvm, gfn);
> +	if (!slot) {
> +		srcu_read_unlock(&kvm->srcu, idx);
> +		return -EINVAL;
> +	}
> +
Also fail if slot->flags & KVM_MEMSLOT_INVALID is true?
There should exist a window for external users to see an invalid slot
when a slot is about to get deleted/moved.
(It happens before MOVE is rejected in kvm_arch_prepare_memory_region()).

> +	write_lock(&kvm->mmu_lock);
> +	__kvm_write_track_add_gfn(kvm, slot, gfn);
> +	write_unlock(&kvm->mmu_lock);
> +
> +	srcu_read_unlock(&kvm->srcu, idx);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
> +
> +/*
> + * remove the guest page from the tracking pool which stops the interception
> + * of corresponding access on that page.
> + *
> + * @kvm: the guest instance we are interested in.
> + * @gfn: the guest page.
> + */
> +int kvm_write_track_remove_gfn(struct kvm *kvm, gfn_t gfn)
> +{
> +	struct kvm_memory_slot *slot;
> +	int idx;
> +
> +	idx = srcu_read_lock(&kvm->srcu);
> +
> +	slot = gfn_to_memslot(kvm, gfn);
> +	if (!slot) {
> +		srcu_read_unlock(&kvm->srcu, idx);
> +		return -EINVAL;
> +	}
> +
Ditto.

> +	write_lock(&kvm->mmu_lock);
> +	__kvm_write_track_remove_gfn(kvm, slot, gfn);
> +	write_unlock(&kvm->mmu_lock);
> +
> +	srcu_read_unlock(&kvm->srcu, idx);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_write_track_remove_gfn);