From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 48FF5C433F5 for ; Wed, 29 Sep 2021 23:21:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 26B3261504 for ; Wed, 29 Sep 2021 23:21:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347520AbhI2XWy (ORCPT ); Wed, 29 Sep 2021 19:22:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1347505AbhI2XWx (ORCPT ); Wed, 29 Sep 2021 19:22:53 -0400 Received: from mail-qv1-xf2f.google.com (mail-qv1-xf2f.google.com [IPv6:2607:f8b0:4864:20::f2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6DF54C06176C for ; Wed, 29 Sep 2021 16:21:11 -0700 (PDT) Received: by mail-qv1-xf2f.google.com with SMTP id dk4so2515643qvb.2 for ; Wed, 29 Sep 2021 16:21:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=vURlTPvciLNHVwm+qpgsVwGxUhwNfUJPxfecQWzYJYA=; b=Zj4wWBdj3VdNHSQijjwB6d/B3Z0yaCN8DLkQcxtzl1osWudJFB0cEUVGPKm3xAsaSO HAOWJFSL0bavVQUI0mkFRIWZCyMFsO+STG0IJHU/nSxslRhlvXPgAxlcy+Ci6caw+Z6d qgJ9x+zAprvCKR0pseEjjuHFnYOORSg847Q4TTGYP+yH+tG3MwHf/9b7whw+grtiqA1M znK7SI7VWx2TjKhDixK8WX2KKNeL4YOkI2oMVStoZVnsQm2iJzHjHx8UMmMVmhJTS/Ka QqWnrgWcNOccgipN9UllCHzX852wNHqdchB2nxleAJaYT7DDZN85NjS6IiTjaZw5impT tdBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=vURlTPvciLNHVwm+qpgsVwGxUhwNfUJPxfecQWzYJYA=; b=rugzX7onegy4BeDC+ie5rBk4D5LfRoC7pT/ij3eeyNTACBtw++0+9yEk4S9bE7kG4Q ZDIwhX7B7gv4TxcS4thSsnCOoTCR1vtOkj0/0ftVw+7gpLoJjDmOt29W0XzocHxImOsm Q9rppaGY7uzxJC2eV8nYCFv6bPKVrk/i9JB2Ik1wkpLM9i3BJ0RJZXZt8+6pNYXbqvRJ grppTlM7opu2BQouPrkd1l41vw8RLI0p1i/xSjRKlc3kRspHkNEvZ5dKbb28F7iSqmES rt47WWR9JRSaZNjhJ1ptDAGkwwOeXCMKoz4iKep9RGhiwna/nUZg/NTUWKfjqRpEyvxo 9R6w== X-Gm-Message-State: AOAM533FFT+eLzlliyiKzrd2GxMOpA3vmwavYAV/hMcPoBAJoV/PLH1m pAB3W8AkOKMP4roV3V9nWbSxOw== X-Google-Smtp-Source: ABdhPJwA55qGt9RWeuL6e34LCWU3u3YFVjjxfHPaXpdwUVW8hGe1+xdfhpM0nZTosoDMpP4WenkAkw== X-Received: by 2002:a0c:c2c4:: with SMTP id c4mr2519771qvi.30.1632957670497; Wed, 29 Sep 2021 16:21:10 -0700 (PDT) Received: from ziepe.ca (hlfxns017vw-142-162-113-129.dhcp-dynamic.fibreop.ns.bellaliant.net. [142.162.113.129]) by smtp.gmail.com with ESMTPSA id i11sm469774qki.28.2021.09.29.16.21.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Sep 2021 16:21:10 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1mVisv-007ihB-2W; Wed, 29 Sep 2021 20:21:09 -0300 Date: Wed, 29 Sep 2021 20:21:09 -0300 From: Jason Gunthorpe To: Max Gurtovoy Cc: Alex Williamson , Leon Romanovsky , Doug Ledford , Yishai Hadas , Bjorn Helgaas , "David S. Miller" , Jakub Kicinski , Kirti Wankhede , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, Saeed Mahameed , Cornelia Huck Subject: Re: [PATCH mlx5-next 2/7] vfio: Add an API to check migration state transition validity Message-ID: <20210929232109.GC3544071@ziepe.ca> References: <20210927231239.GE3544071@ziepe.ca> <25c97be6-eb4a-fdc8-3ac1-5628073f0214@nvidia.com> <20210929063551.47590fbb.alex.williamson@redhat.com> <1eba059c-4743-4675-9f72-1a26b8f3c0f6@nvidia.com> <20210929075019.48d07deb.alex.williamson@redhat.com> <20210929091712.6390141c.alex.williamson@redhat.com> <20210929161433.GA1808627@ziepe.ca> <29835bf4-d094-ae6d-1a32-08e65847b52c@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <29835bf4-d094-ae6d-1a32-08e65847b52c@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Sep 30, 2021 at 12:48:55AM +0300, Max Gurtovoy wrote: > > On 9/29/2021 7:14 PM, Jason Gunthorpe wrote: > > On Wed, Sep 29, 2021 at 06:28:44PM +0300, Max Gurtovoy wrote: > > > > > > So you have a device that's actively modifying its internal state, > > > > performing I/O, including DMA (thereby dirtying VM memory), all while > > > > in the _STOP state? And you don't see this as a problem? > > > I don't see how is it different from vfio-pci situation. > > vfio-pci provides no way to observe the migration state. It isn't > > "000b" > > Alex said that there is a problem of compatibility. Yes, when a vfio_device first opens it must be running - ie able to do DMA and otherwise operational. When we add the migration extension this cannot change, so after open_device() the device should be operational. The reported state in the migration region should accurately reflect what the device is currently doing. If the device is operational then it must report running, not stopped. Thus a driver cannot just zero initalize the migration "registers", they have to be accurate. > > > Maybe we need to rename STOP state. We can call it READY or LIVE or > > > NON_MIGRATION_STATE. > > It was a poor choice to use 000b as stop, but it doesn't really > > matter. The mlx5 driver should just pre-init this readable to running. > > I guess we can do it for this reason. There is no functional problem nor > compatibility issue here as was mentioned. > > But still we need the kernel to track transitions. We don't want to allow > moving from RESUMING to SAVING state for example. How this transition can be > allowed ? It seems semantically fine to me, as per Alex's note what will happen is defined: driver will see RESUMING toggle off so it will trigger a de-serialization driver will see SAVING toggled on so it will serialize the new state (either the pre-copy state or the post-copy state dpending on the running bit) Depending on the running bit the device may or may not be woken up. If de-serialization fails then the state goes to error and SAVING is ignored. The driver logic probably looks something like this: // Running toggles off if (oldstate & RUNNING != newstate & RUNNING && oldstate & RUNNING) queice freeze // Resuming toggles off if (oldstate & RESUMING != newstate & RESUMING && oldstate & RESUMING) deserialize // Saving toggles on if (oldstate & SAVING != newstate & SAVING && newstate & SAVING) if (!(newstate & RUNNING)) serialize post copy // Running toggles on if (oldstate & RUNNING != newstate & RUNNING && newstate & RUNNING) unfreeze unqueice I'd have to check that carefully against the state chart from my last email though.. And need to check how the "Stop Active Transactions" bit fits in there Jason