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Tsirkin" , Richard Henderson , qemu-level , Gautam Dawar , Markus Armbruster , Eduardo Habkost , Harpreet Singh Anand , Xiao W Wang , Stefan Hajnoczi , Eli Cohen , Paolo Bonzini , Zhu Lingshan , virtualization , Eric Blake X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" T24gVHVlLCBGZWIgMjIsIDIwMjIgYXQgNDowNiBQTSBFdWdlbmlvIFBlcmV6IE1hcnRpbgo8ZXBl cmV6bWFAcmVkaGF0LmNvbT4gd3JvdGU6Cj4KPiBPbiBUdWUsIEZlYiAyMiwgMjAyMiBhdCA4OjQx IEFNIEphc29uIFdhbmcgPGphc293YW5nQHJlZGhhdC5jb20+IHdyb3RlOgo+ID4KPiA+Cj4gPiDl nKggMjAyMi8yLzE3IOS4i+WNiDQ6MjIsIEV1Z2VuaW8gUGVyZXogTWFydGluIOWGmemBkzoKPiA+ ID4gT24gVGh1LCBGZWIgMTcsIDIwMjIgYXQgNzowMiBBTSBKYXNvbiBXYW5nIDxqYXNvd2FuZ0By 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Tue, 22 Feb 2022 19:46:57 -0800 (PST) MIME-Version: 1.0 References: <20220121202733.404989-1-eperezma@redhat.com> <20220121202733.404989-29-eperezma@redhat.com> <42664143-6d0c-b107-ec90-8e6336bae29b@redhat.com> <9b32f664-56a9-3718-cf48-49003f87d430@redhat.com> <0f0204f1-8b7f-a21e-495e-24443a63f026@redhat.com> In-Reply-To: From: Jason Wang Date: Wed, 23 Feb 2022 11:46:46 +0800 Message-ID: Subject: Re: [PATCH 28/31] vdpa: Expose VHOST_F_LOG_ALL on SVQ To: Eugenio Perez Martin Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=jasowang@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=170.10.133.124; envelope-from=jasowang@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Parav Pandit , Cindy Lu , "Michael S. Tsirkin" , Juan Quintela , Richard Henderson , qemu-level , Gautam Dawar , Markus Armbruster , Eduardo Habkost , Harpreet Singh Anand , Xiao W Wang , Peter Xu , Stefan Hajnoczi , Eli Cohen , Paolo Bonzini , Zhu Lingshan , virtualization , Eric Blake , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Feb 22, 2022 at 4:06 PM Eugenio Perez Martin wrote: > > On Tue, Feb 22, 2022 at 8:41 AM Jason Wang wrote: > > > > > > =E5=9C=A8 2022/2/17 =E4=B8=8B=E5=8D=884:22, Eugenio Perez Martin =E5=86= =99=E9=81=93: > > > On Thu, Feb 17, 2022 at 7:02 AM Jason Wang wrot= e: > > >> On Wed, Feb 16, 2022 at 11:54 PM Eugenio Perez Martin > > >> wrote: > > >>> On Tue, Feb 8, 2022 at 9:25 AM Jason Wang wro= te: > > >>>> > > >>>> =E5=9C=A8 2022/2/1 =E4=B8=8B=E5=8D=887:45, Eugenio Perez Martin = =E5=86=99=E9=81=93: > > >>>>> On Sun, Jan 30, 2022 at 7:50 AM Jason Wang = wrote: > > >>>>>> =E5=9C=A8 2022/1/22 =E4=B8=8A=E5=8D=884:27, Eugenio P=C3=A9rez = =E5=86=99=E9=81=93: > > >>>>>>> SVQ is able to log the dirty bits by itself, so let's use it to= not > > >>>>>>> block migration. > > >>>>>>> > > >>>>>>> Also, ignore set and clear of VHOST_F_LOG_ALL on set_features i= f SVQ is > > >>>>>>> enabled. Even if the device supports it, the reports would be n= onsense > > >>>>>>> because SVQ memory is in the qemu region. > > >>>>>>> > > >>>>>>> The log region is still allocated. Future changes might skip th= at, but > > >>>>>>> this series is already long enough. > > >>>>>>> > > >>>>>>> Signed-off-by: Eugenio P=C3=A9rez > > >>>>>>> --- > > >>>>>>> hw/virtio/vhost-vdpa.c | 20 ++++++++++++++++++++ > > >>>>>>> 1 file changed, 20 insertions(+) > > >>>>>>> > > >>>>>>> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c > > >>>>>>> index fb0a338baa..75090d65e8 100644 > > >>>>>>> --- a/hw/virtio/vhost-vdpa.c > > >>>>>>> +++ b/hw/virtio/vhost-vdpa.c > > >>>>>>> @@ -1022,6 +1022,9 @@ static int vhost_vdpa_get_features(struct= vhost_dev *dev, uint64_t *features) > > >>>>>>> if (ret =3D=3D 0 && v->shadow_vqs_enabled) { > > >>>>>>> /* Filter only features that SVQ can offer to guest= */ > > >>>>>>> vhost_svq_valid_guest_features(features); > > >>>>>>> + > > >>>>>>> + /* Add SVQ logging capabilities */ > > >>>>>>> + *features |=3D BIT_ULL(VHOST_F_LOG_ALL); > > >>>>>>> } > > >>>>>>> > > >>>>>>> return ret; > > >>>>>>> @@ -1039,8 +1042,25 @@ static int vhost_vdpa_set_features(struc= t vhost_dev *dev, > > >>>>>>> > > >>>>>>> if (v->shadow_vqs_enabled) { > > >>>>>>> uint64_t dev_features, svq_features, acked_features= ; > > >>>>>>> + uint8_t status =3D 0; > > >>>>>>> bool ok; > > >>>>>>> > > >>>>>>> + ret =3D vhost_vdpa_call(dev, VHOST_VDPA_GET_STATUS, &s= tatus); > > >>>>>>> + if (unlikely(ret)) { > > >>>>>>> + return ret; > > >>>>>>> + } > > >>>>>>> + > > >>>>>>> + if (status & VIRTIO_CONFIG_S_DRIVER_OK) { > > >>>>>>> + /* > > >>>>>>> + * vhost is trying to enable or disable _F_LOG, an= d the device > > >>>>>>> + * would report wrong dirty pages. SVQ handles it. > > >>>>>>> + */ > > >>>>>> I fail to understand this comment, I'd think there's no way to d= isable > > >>>>>> dirty page tracking for SVQ. > > >>>>>> > > >>>>> vhost_log_global_{start,stop} are called at the beginning and end= of > > >>>>> migration. To inform the device that it should start logging, the= y set > > >>>>> or clean VHOST_F_LOG_ALL at vhost_dev_set_log. > > >>>> > > >>>> Yes, but for SVQ, we can't disable dirty page tracking, isn't it? = The > > >>>> only thing is to ignore or filter out the F_LOG_ALL and pretend to= be > > >>>> enabled and disabled. > > >>>> > > >>> Yes, that's what this patch does. > > >>> > > >>>>> While SVQ does not use VHOST_F_LOG_ALL, it exports the feature bi= t so > > >>>>> vhost does not block migration. Maybe we need to look for another= way > > >>>>> to do this? > > >>>> > > >>>> I'm fine with filtering since it's much more simpler, but I fail t= o > > >>>> understand why we need to check DRIVER_OK. > > >>>> > > >>> Ok maybe I can make that part more clear, > > >>> > > >>> Since both operations use vhost_vdpa_set_features we must just filt= er > > >>> the one that actually sets or removes VHOST_F_LOG_ALL, without > > >>> affecting other features. > > >>> > > >>> In practice, that means to not forward the set features after > > >>> DRIVER_OK. The device is not expecting them anymore. > > >> I wonder what happens if we don't do this. > > >> > > > If we simply delete the check vhost_dev_set_features will return an > > > error, failing the start of the migration. More on this below. > > > > > > Ok. > > > > > > > > > >> So kernel had this check: > > >> > > >> /* > > >> * It's not allowed to change the features after they have > > >> * been negotiated. > > >> */ > > >> if (ops->get_status(vdpa) & VIRTIO_CONFIG_S_FEATURES_OK) > > >> return -EBUSY; > > >> > > >> So is it FEATURES_OK actually? > > >> > > > Yes, FEATURES_OK seems more appropriate actually so I will switch to > > > it for the next version. > > > > > > But it should be functionally equivalent, since > > > vhost.c:vhost_dev_start sets both and the setting of _F_LOG_ALL canno= t > > > be concurrent with it. > > > > > > Right. > > > > > > > > > >> For this patch, I wonder if the thing we need to do is to see whethe= r > > >> it is a enable/disable F_LOG_ALL and simply return. > > >> > > > Yes, that's the intention of the patch. > > > > > > We have 4 cases here: > > > a) We're being called from vhost_dev_start, with enable_log =3D false > > > b) We're being called from vhost_dev_start, with enable_log =3D true > > > > > > And this case makes us can't simply return without calling vhost-vdpa. > > > > It calls because {FEATURES,DRIVER}_OK is still not set at that point. > > > > > > c) We're being called from vhost_dev_set_log, with enable_log =3D fal= se > > > d) We're being called from vhost_dev_set_log, with enable_log =3D tru= e > > > > > > The way to tell the difference between a/b and c/d is to check if > > > {FEATURES,DRIVER}_OK is set. And, as you point out in previous mails, > > > F_LOG_ALL must be filtered unconditionally since SVQ tracks dirty > > > memory through the memory unmapping, so we clear the bit > > > unconditionally if we detect that VHOST_SET_FEATURES will be called > > > (cases a and b). > > > > > > Another possibility is to track if features have been set with a bool > > > in vhost_vdpa or something like that. But it seems cleaner to me to > > > only store that in the actual device. > > > > > > So I suggest to make sure codes match the comment: > > > > if (status & VIRTIO_CONFIG_S_DRIVER_OK) { > > /* > > * vhost is trying to enable or disable _F_LOG, and the de= vice > > * would report wrong dirty pages. SVQ handles it. > > */ > > return 0; > > } > > > > It would be better to check whether the caller is toggling _F_LOG_ALL i= n > > this case. > > > > How to detect? We can save feature flags and compare, but ignoring all > set_features after FEATURES_OK seems simpler to me. Something like: (status ^ status_old =3D=3D _F_LOG_ALL) ? It helps us to return errors on wrong features set during DRIVER_OK. Thanks > > Would changing the comment work? Something like "set_features after > _S_FEATURES_OK means vhost is trying to enable or disable _F_LOG, and > the device would report wrong dirty pages. SVQ handles it." > > Thanks! > > > Thanks > > > > > > > > > >> Thanks > > >> > > >>> Does that make more sense? > > >>> > > >>> Thanks! > > >>> > > >>>> Thanks > > >>>> > > >>>> > > >>>>> Thanks! > > >>>>> > > >>>>>> Thanks > > >>>>>> > > >>>>>> > > >>>>>>> + return 0; > > >>>>>>> + } > > >>>>>>> + > > >>>>>>> + /* We must not ack _F_LOG if SVQ is enabled */ > > >>>>>>> + features &=3D ~BIT_ULL(VHOST_F_LOG_ALL); > > >>>>>>> + > > >>>>>>> ret =3D vhost_vdpa_get_dev_features(dev, &dev_featu= res); > > >>>>>>> if (ret !=3D 0) { > > >>>>>>> error_report("Can't get vdpa device features, g= ot (%d)", ret); > > >