Date:   Mon, 22 Nov 2021 17:16:47 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Chao Peng <chao.p.peng@linux.intel.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        qemu-devel@nongnu.org, Wanpeng Li <wanpengli@tencent.com>,
        jun.nakajima@intel.com, david@redhat.com,
        "J . Bruce Fields" <bfields@fieldses.org>, dave.hansen@intel.com,
        "H . Peter Anvin" <hpa@zytor.com>, ak@linux.intel.com,
        Jonathan Corbet <corbet@lwn.net>,
        Joerg Roedel <joro@8bytes.org>, x86@kernel.org,
        Hugh Dickins <hughd@google.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        luto@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Sean Christopherson <seanjc@google.com>, susie.li@intel.com,
        Jeff Layton <jlayton@kernel.org>, john.ji@intel.com,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC v2 PATCH 13/13] KVM: Enable memfd based page
 invalidation/fallocate
Message-ID: <20211122141647.3pcsywilrzcoqvbf@box.shutemov.name>
References: <20211119134739.20218-1-chao.p.peng@linux.intel.com>
 <20211119134739.20218-14-chao.p.peng@linux.intel.com>
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In-Reply-To: <20211119134739.20218-14-chao.p.peng@linux.intel.com>
Precedence: bulk

On Fri, Nov 19, 2021 at 09:47:39PM +0800, Chao Peng wrote:
> Since the memory backing store does not get notified when VM is
> destroyed so need check if VM is still live in these callbacks.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
>  virt/kvm/memfd.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/virt/kvm/memfd.c b/virt/kvm/memfd.c
> index bd930dcb455f..bcfdc685ce22 100644
> --- a/virt/kvm/memfd.c
> +++ b/virt/kvm/memfd.c
> @@ -12,16 +12,38 @@
>  #include <linux/memfd.h>
>  const static struct guest_mem_ops *memfd_ops;
>  
> +static bool vm_is_dead(struct kvm *vm)
> +{
> +	struct kvm *kvm;
> +
> +	list_for_each_entry(kvm, &vm_list, vm_list) {
> +		if (kvm == vm)
> +			return false;
> +	}

I don't think this is enough. The struct kvm can be freed and re-allocated
from the slab and this function will give false-negetive.

Maybe the kvm has to be tagged with a sequential id that incremented every
allocation. This id can be checked here.

> +
> +	return true;
> +}

-- 
 Kirill A. Shutemov