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[62.219.155.47]) by smtp.gmail.com with ESMTPSA id y12sm1133427wrw.88.2020.02.10.08.04.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Feb 2020 08:04:30 -0800 (PST) Date: Mon, 10 Feb 2020 11:04:28 -0500 From: "Michael S. Tsirkin" To: Raphael Norwitz Subject: Re: [PATCH v2 0/3] vhost-user: Lift Max Ram Slots Limitation Message-ID: <20200210110330-mutt-send-email-mst@kernel.org> References: <1579143426-18305-1-git-send-email-raphael.norwitz@nutanix.com> <20200206033248-mutt-send-email-mst@kernel.org> <20200209171442.GA14809@localhost.localdomain> MIME-Version: 1.0 In-Reply-To: <20200209171442.GA14809@localhost.localdomain> X-MC-Unique: kwOJe7xCP6WSvko1X8de2A-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Sun, Feb 09, 2020 at 12:14:42PM -0500, Raphael Norwitz wrote: > On Thu, Feb 06, 2020 at 03:33:13AM -0500, Michael S. Tsirkin wrote: > >=20 > > On Wed, Jan 15, 2020 at 09:57:03PM -0500, Raphael Norwitz wrote: > > >=20 > > > Changes since V1: > > > * Kept the assert in vhost_user_set_mem_table_postcopy, but moved= it > > > to prevent corruption > > > * Made QEMU send a single VHOST_USER_GET_MAX_MEMSLOTS message at > > > startup and cache the returned value so that QEMU does not need= to > > > query the backend every time vhost_backend_memslots_limit is ca= lled. > >=20 > > I'm a bit confused about what happens on reconnect. > > Can you clarify pls? > >=20 > >From what I can see, backends which support reconnect call vhost_dev_ini= t, > which then calls vhost_user_backend_init(), as vhost-user-blk does here: > https://github.com/qemu/qemu/blob/master/hw/block/vhost-user-blk.c#L315. = The > ram slots limit is fetched in vhost_user_backend_init() so every time the > device reconnects the limit should be refetched.=20 Right. Point is, we might have validated using an old limit. Reconnect needs to verify limit did not change or at least did not decrease. --=20 MST