linux-kernel - Re: [RFC v2 PATCH 09/13] KVM: Introduce kvm_memfd_invalidate

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Date:   Tue, 23 Nov 2021 09:46:34 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, qemu-devel@...gnu.org
Cc:     Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, john.ji@...el.com, susie.li@...el.com,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com,
        david@...hat.com
Subject: Re: [RFC v2 PATCH 09/13] KVM: Introduce kvm_memfd_invalidate_range

On 11/19/21 14:47, Chao Peng wrote:
> +
> +	/* Prevent memslot modification */
> +	spin_lock(&kvm->mn_invalidate_lock);
> +	kvm->mn_active_invalidate_count++;
> +	spin_unlock(&kvm->mn_invalidate_lock);
> +
> +	ret = __kvm_handle_useraddr_range(kvm, &useraddr_range);
> +
> +	spin_lock(&kvm->mn_invalidate_lock);
> +	kvm->mn_active_invalidate_count--;
> +	spin_unlock(&kvm->mn_invalidate_lock);
> +


You need to follow this with a rcuwait_wake_up as in 
kvm_mmu_notifier_invalidate_range_end.

It's probably best if you move the manipulations of 
mn_active_invalidate_count from kvm_mmu_notifier_invalidate_range_* to 
two separate functions.

Paolo