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bh=phpUApLFWJcRZKTgToVV/F1hUfJLo3qn5Y2gqdT+Elw=; b=Ct3HTrBKFpZE4Zlead+wTuEfSAjvkoqJTKKR+9biXx+4CJuKX2ZkmtOTA4uoOUYLzr6EFO GZRaMR2JNNIOldre9k7fyDMRcaXVsqnFvGS0uWYfYWdqaMkCi9T4pfVNjdkevdgHxpQ+qe w4yn0SbfACZoHe46ZZeK8fUO6PU5kDI= X-MC-Unique: Jy9EJ1jVOdSwzOX9Nyz_iQ-1 From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v4 06/11] vfio: Sanity check maximum number of DMA mappings with RamDiscardMgr Date: Thu, 7 Jan 2021 14:34:18 +0100 Message-Id: <20210107133423.44964-7-david@redhat.com> In-Reply-To: <20210107133423.44964-1-david@redhat.com> References: <20210107133423.44964-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.246, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Pankaj Gupta , Wei Yang , David Hildenbrand , "Michael S. Tsirkin" , "Dr . David Alan Gilbert" , Peter Xu , Marek Kedzierski , Auger Eric , Alex Williamson , teawater , Jonathan Cameron , Paolo Bonzini , Igor Mammedov Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Although RamDiscardMgr can handle running into the maximum number of DMA mappings by propagating errors when creating a DMA mapping, we want to sanity check and warn the user early that there is a theoretical setup issue and that virtio-mem might not be able to provide as much memory towards a VM as desired. As suggested by Alex, let's use the number of KVM memory slots to guess how many other mappings we might see over time. Cc: Paolo Bonzini Cc: "Michael S. Tsirkin" Cc: Alex Williamson Cc: Dr. David Alan Gilbert Cc: Igor Mammedov Cc: Pankaj Gupta Cc: Peter Xu Cc: Auger Eric Cc: Wei Yang Cc: teawater Cc: Marek Kedzierski Signed-off-by: David Hildenbrand --- hw/vfio/common.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/hw/vfio/common.c b/hw/vfio/common.c index 1babb6bb99..bc20f738ce 100644 --- a/hw/vfio/common.c +++ b/hw/vfio/common.c @@ -758,6 +758,49 @@ static void vfio_register_ram_discard_notifier(VFIOCon= tainer *container, vfio_ram_discard_notify_discard_all); rdmc->register_listener(rdm, section->mr, &vrdl->listener); QLIST_INSERT_HEAD(&container->vrdl_list, vrdl, next); + + /* + * Sanity-check if we have a theoretically problematic setup where we = could + * exceed the maximum number of possible DMA mappings over time. We as= sume + * that each mapped section in the same address space as a RamDiscardM= gr + * section consumes exactly one DMA mapping, with the exception of + * RamDiscardMgr sections; i.e., we don't expect to have gIOMMU sectio= ns in + * the same address space as RamDiscardMgr sections. + * + * We assume that each section in the address space consumes one memsl= ot. + * We take the number of KVM memory slots as a best guess for the maxi= mum + * number of sections in the address space we could have over time, + * also consuming DMA mappings. + */ + if (container->dma_max_mappings) { + unsigned int vrdl_count =3D 0, vrdl_mappings =3D 0, max_memslots = =3D 512; + +#ifdef CONFIG_KVM + if (kvm_enabled()) { + max_memslots =3D kvm_get_max_memslots(); + } +#endif + + QLIST_FOREACH(vrdl, &container->vrdl_list, next) { + hwaddr start, end; + + start =3D QEMU_ALIGN_DOWN(vrdl->offset_within_address_space, + vrdl->granularity); + end =3D ROUND_UP(vrdl->offset_within_address_space + vrdl->siz= e, + vrdl->granularity); + vrdl_mappings =3D (end - start) / vrdl->granularity; + vrdl_count++; + } + + if (vrdl_mappings + max_memslots - vrdl_count > + container->dma_max_mappings) { + warn_report("%s: possibly running out of DMA mappings. E.g., t= ry" + " increasing the 'block-size' of virtio-mem devies= ." + " Maximum possible DMA mappings: %d, Maximum possi= ble" + " memslots: %d", __func__, container->dma_max_mapp= ings, + max_memslots); + } + } } =20 static void vfio_unregister_ram_discard_listener(VFIOContainer *container, --=20 2.29.2