Re: [PATCH net] vsock: forward all packets to the host when no H2G is registered

From: Alexander Graf <graf@amazon.com>
To: Stefan Hajnoczi <stefanha@redhat.com>,
	Stefano Garzarella <sgarzare@redhat.com>
Cc: <netdev@vger.kernel.org>, Jorgen Hansen <jhansen@vmware.com>,
	"David S. Miller" <davem@davemloft.net>,
	Dexuan Cui <decui@microsoft.com>,
	"Anthony Liguori" <aliguori@amazon.com>,
	David Duncan <davdunc@amazon.com>,
	"Andra Paraschiv" <andraprs@amazon.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jakub Kicinski <kuba@kernel.org>, <linux-kernel@vger.kernel.org>,
	"Alexander Graf" <graf@amazon.de>
Subject: Re: [PATCH net] vsock: forward all packets to the host when no H2G is registered
Date: Thu, 19 Nov 2020 15:25:42 +0100	[thread overview]
Message-ID: <ffdc9e0c-fee2-e334-053b-0a26305b55ae@amazon.com> (raw)
In-Reply-To: <20201119140359.GE838210@stefanha-x1.localdomain>

On 19.11.20 15:03, Stefan Hajnoczi wrote:
> On Thu, Nov 12, 2020 at 02:38:37PM +0100, Stefano Garzarella wrote:
>> Before commit c0cfa2d8a788 ("vsock: add multi-transports support"),
>> if a G2H transport was loaded (e.g. virtio transport), every packets
>> was forwarded to the host, regardless of the destination CID.
>> The H2G transports implemented until then (vhost-vsock, VMCI) always
>> responded with an error, if the destination CID was not
>> VMADDR_CID_HOST.
>>
>>  From that commit, we are using the remote CID to decide which
>> transport to use, so packets with remote CID > VMADDR_CID_HOST(2)
>> are sent only through H2G transport. If no H2G is available, packets
>> are discarded directly in the guest.
>>
>> Some use cases (e.g. Nitro Enclaves [1]) rely on the old behaviour
>> to implement sibling VMs communication, so we restore the old
>> behavior when no H2G is registered.
>> It will be up to the host to discard packets if the destination is
>> not the right one. As it was already implemented before adding
>> multi-transport support.
>>
>> Tested with nested QEMU/KVM by me and Nitro Enclaves by Andra.
>>
>> [1] Documentation/virt/ne_overview.rst
>>
>> Cc: Jorgen Hansen <jhansen@vmware.com>
>> Cc: Dexuan Cui <decui@microsoft.com>
>> Fixes: c0cfa2d8a788 ("vsock: add multi-transports support")
>> Reported-by: Andra Paraschiv <andraprs@amazon.com>
>> Tested-by: Andra Paraschiv <andraprs@amazon.com>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>> ---
>>   net/vmw_vsock/af_vsock.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

Is there anything we have to do to also get this into the affected 
stable trees? :)

Alex

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