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auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eperezma@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=205.139.110.120; envelope-from=eperezma@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/11 02:18:06 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Peter Maydell , Yan Zhao , Juan Quintela , Jason Wang , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Eric Auger , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Aug 11, 2020 at 7:01 PM Eugenio Perez Martin wrote: > > On Fri, Jun 26, 2020 at 11:29 PM Peter Xu wrote: > > > > Hi, Eugenio, > > > > (CCing Eric, Yan and Michael too) > > > > On Fri, Jun 26, 2020 at 08:41:22AM +0200, Eugenio P=C3=A9rez wrote: > > > diff --git a/memory.c b/memory.c > > > index 2f15a4b250..7f789710d2 100644 > > > --- a/memory.c > > > +++ b/memory.c > > > @@ -1915,8 +1915,6 @@ void memory_region_notify_one(IOMMUNotifier *no= tifier, > > > return; > > > } > > > > > > - assert(entry->iova >=3D notifier->start && entry_end <=3D notifi= er->end); > > > > I can understand removing the assertion should solve the issue, however= imho > > the major issue is not about this single assertion but the whole addr_m= ask > > issue behind with virtio... > > > > For normal IOTLB invalidations, we were trying our best to always make > > IOMMUTLBEntry contain a valid addr_mask to be 2**N-1. E.g., that's wha= t we're > > doing with the loop in vtd_address_space_unmap(). > > > > But this is not the first time that we may want to break this assumptio= n for > > virtio so that we make the IOTLB a tuple of (start, len), then that len= can be > > not a address mask any more. That seems to be more efficient for thing= s like > > vhost because iotlbs there are not page based, so it'll be inefficient = if we > > always guarantee the addr_mask because it'll be quite a lot more roundt= rips of > > the same range of invalidation. Here we've encountered another issue o= f > > triggering the assertion with virtio-net, but only with the old RHEL7 g= uest. > > > > I'm thinking whether we can make the IOTLB invalidation configurable by > > specifying whether the backend of the notifier can handle arbitary addr= ess > > range in some way. So we still have the guaranteed addr_masks by defau= lt > > (since I still don't think totally break the addr_mask restriction is w= ise...), > > however we can allow the special backends to take adavantage of using a= rbitary > > (start, len) ranges for reasons like performance. > > > > To do that, a quick idea is to introduce a flag IOMMU_NOTIFIER_ARBITRAR= Y_MASK > > to IOMMUNotifierFlag, to declare that the iommu notifier (and its backe= nd) can > > take arbitrary address mask, then it can be any value and finally becom= es a > > length rather than an addr_mask. Then for every iommu notify() we can = directly > > deliver whatever we've got from the upper layer to this notifier. With= the new > > flag, vhost can do iommu_notifier_init() with UNMAP|ARBITRARY_MASK so i= t > > declares this capability. Then no matter for device iotlb or normal io= tlb, we > > skip the complicated procedure to split a big range into small ranges t= hat are > > with strict addr_mask, but directly deliver the message to the iommu no= tifier. > > E.g., we can skip the loop in vtd_address_space_unmap() if the notifier= is with > > ARBITRARY flag set. > > > > Then, the assert() is not accurate either, and may become something lik= e: > > > > diff --git a/memory.c b/memory.c > > index 2f15a4b250..99d0492509 100644 > > --- a/memory.c > > +++ b/memory.c > > @@ -1906,6 +1906,7 @@ void memory_region_notify_one(IOMMUNotifier *noti= fier, > > { > > IOMMUNotifierFlag request_flags; > > hwaddr entry_end =3D entry->iova + entry->addr_mask; > > + IOMMUTLBEntry tmp =3D *entry; > > > > /* > > * Skip the notification if the notification does not overlap > > @@ -1915,7 +1916,13 @@ void memory_region_notify_one(IOMMUNotifier *not= ifier, > > return; > > } > > > > - assert(entry->iova >=3D notifier->start && entry_end <=3D notifier= ->end); > > + if (notifier->notifier_flags & IOMMU_NOTIFIER_ARBITRARY_MASK) { > > + tmp.iova =3D MAX(tmp.iova, notifier->start); > > Hi! > > If I modify the tmp.iova, the guest will complain (in dmesg): > [ 154.426828] DMAR: DRHD: handling fault status reg 2 > [ 154.427700] DMAR: [DMA Read] Request device [01:00.0] fault addr > ffff90d53fada000 [fault reason 04] Access beyond MGAW > > And will not forward packets anymore on that interface. Guests are > totally ok if I only modify addr_mask. > > Still investigating the issue. > > Thanks! > Sorry it seems that I lost the nitpick Yan pointed out :). Sending RFC v3. > > > + tmp.addr_mask =3D MIN(tmp.addr_mask, notifier->end); > > + assert(tmp.iova <=3D tmp.addr_mask); > > + } else { > > + assert(entry->iova >=3D notifier->start && entry_end <=3D noti= fier->end); > > + } > > > > if (entry->perm & IOMMU_RW) { > > request_flags =3D IOMMU_NOTIFIER_MAP; > > @@ -1924,7 +1931,7 @@ void memory_region_notify_one(IOMMUNotifier *noti= fier, > > } > > > > if (notifier->notifier_flags & request_flags) { > > - notifier->notify(notifier, entry); > > + notifier->notify(notifier, &tmp); > > } > > } > > > > Then we can keep the assert() for e.g. vfio, however vhost can skip it = and even > > get some further performance boosts.. Does that make sense? > > > > Thanks, > > > > -- > > Peter Xu > >