linux-kernel - Re: [PATCH] kvm/vfio: ensure kvg instance stays around in kvm_vfio_group

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Message-ID: <2023073144-whimsical-liberty-4b4f@gregkh>
Date:   Mon, 31 Jul 2023 14:02:59 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Roxana Bradescu <roxabee@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm/vfio: ensure kvg instance stays around in
 kvm_vfio_group_add()

On Mon, Jul 10, 2023 at 03:20:31PM -0700, Dmitry Torokhov wrote:
> kvm_vfio_group_add() creates kvg instance, links it to kv->group_list,
> and calls kvm_vfio_file_set_kvm() with kvg->file as an argument after
> dropping kv->lock. If we race group addition and deletion calls, kvg
> instance may get freed by the time we get around to calling
> kvm_vfio_file_set_kvm().
> 
> Fix this by moving call to kvm_vfio_file_set_kvm() under the protection
> of kv->lock. We already call it while holding the same lock when vfio
> group is being deleted, so it should be safe here as well.
> 
> Fixes: ba70a89f3c2a ("vfio: Change vfio_group_set_kvm() to vfio_file_set_kvm()")
> Cc: stable@...r.kernel.org
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  virt/kvm/vfio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 9584eb57e0ed..cd46d7ef98d6 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -179,10 +179,10 @@ static int kvm_vfio_group_add(struct kvm_device *dev, unsigned int fd)
>  	list_add_tail(&kvg->node, &kv->group_list);
>  
>  	kvm_arch_start_assignment(dev->kvm);
> +	kvm_vfio_file_set_kvm(kvg->file, dev->kvm);
>  
>  	mutex_unlock(&kv->lock);
>  
> -	kvm_vfio_file_set_kvm(kvg->file, dev->kvm);
>  	kvm_vfio_update_coherency(dev);
>  
>  	return 0;
> -- 
> 2.41.0.255.g8b1d071c50-goog

What ever happened to this change?  Did it end up in a KVM tree
somewhere?

thanks,

greg k-h