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[82.53.135.65]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f8635c8d7sm3212686f8f.21.2026.07.22.02.14.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 02:14:26 -0700 (PDT) Date: Wed, 22 Jul 2026 11:14:23 +0200 From: Stefano Garzarella To: Andrey Drobyshev Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, mst@redhat.com, stefanha@redhat.com, dongli.zhang@oracle.com, maciej.szmigiero@oracle.com, bchaney@akamai.com, mark.kanda@oracle.com, ptikhomirov@virtuozzo.com, den@openvz.org Subject: Re: [PATCH v5 2/5] vhost/vsock: suppress EHOSTUNREACH fast-fail during CPR pause Message-ID: References: <20260720102241.371610-1-andrey.drobyshev@virtuozzo.com> <20260720102241.371610-3-andrey.drobyshev@virtuozzo.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260720102241.371610-3-andrey.drobyshev@virtuozzo.com> On Mon, Jul 20, 2026 at 01:22:38PM +0300, Andrey Drobyshev wrote: >Earlier commit bb26ed5f3a8b ("vhost/vsock: Refuse the connection >immediately when guest isn't ready") added a fast-fail in >vhost_transport_send_pkt(). It rejects every host send with -EHOSTUNREACH >until the destination calls SET_RUNNING(1). The fast-fail condition checks >whether device's backends are dropped, and if they're, the guest is >considered to be not ready. > >However, there might be other reasons for backends to be nulled. In >particular, when QEMU is performing CPR (checkpoint-restore) migration, >device ownership is being RESET and SET again, which leads to backends >drop and reattach. If we end up connecting during this window, an >AF_VSOCK client gets -EHOSTUNREACH, which is wrong. > >Add an 'ever_started' flag which is set once in vhost_vsock_start() and is >never cleared. The behaviour changes to: > > * When device was never started -> flag is unset -> no listener can > exist yet -> fast-fail; > * Once the device starts -> flag is set -> we don't fast-fail -> > we queue and preserve during any later stop / CPR pause. > >The VHOST_RESET_OWNER ioctl is implemented in a following patch, and >without RESET_OWNER the problem we fix here isn't manifesting - thus >this patch is a preparation to support RESET_OWNER. > >Important caveat: after the first start, a connect during any stopped >window is queued instead of fast-failed. That was the behaviour before >the patch bb26ed5f3a8b, and we're restoring it now. However we still >keep the behaviour originally intended by that commit (i.e. fast-fail if >there's no real listener yet) while fixing the CPR path. > >Suggested-by: Stefano Garzarella >Signed-off-by: Denis V. Lunev >Signed-off-by: Andrey Drobyshev >Reviewed-by: Pavel Tikhomirov >--- > drivers/vhost/vsock.c | 22 ++++++++++++---------- > 1 file changed, 12 insertions(+), 10 deletions(-) Reviewed-by: Stefano Garzarella