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Mon, 27 Jul 2020 16:47:54 +0000 (UTC) Date: Mon, 27 Jul 2020 10:47:54 -0600 From: Alex Williamson To: Pierre Morel Subject: Re: [RFC PATCH] s390x/pci: vfio-pci breakage with disabled mem enforcement Message-ID: <20200727104754.4337818c@x1.home> In-Reply-To: <0481c77e-f71f-886b-9b0a-41529eb139ee@linux.ibm.com> References: <1595517236-17823-1-git-send-email-mjrosato@linux.ibm.com> <20200723102916.7cf15b43@w520.home> <0481c77e-f71f-886b-9b0a-41529eb139ee@linux.ibm.com> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=alex.williamson@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 01:44:14 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 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_H2=-1, 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: schnelle@linux.ibm.com, Matthew Rosato , david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 27 Jul 2020 17:40:39 +0200 Pierre Morel wrote: > On 2020-07-23 18:29, Alex Williamson wrote: > > On Thu, 23 Jul 2020 11:13:55 -0400 > > Matthew Rosato wrote: > > > >> I noticed that after kernel commit abafbc55 'vfio-pci: Invalidate mmaps > >> and block MMIO access on disabled memory' vfio-pci via qemu on s390x > >> fails spectacularly, with errors in qemu like: > >> > >> qemu-system-s390x: vfio_region_read(0001:00:00.0:region0+0x0, 4) failed: Input/output error > >> > >> From read to bar 0 originating out of hw/s390x/s390-pci-inst.c:zpci_read_bar(). > >> > >> So, I'm trying to figure out how to get vfio-pci happy again on s390x. From > >> a bit of tracing, we seem to be triggering the new trap in > >> __vfio_pci_memory_enabled(). Sure enough, if I just force this function to > >> return 'true' as a test case, things work again. > >> The included patch attempts to enforce the setting, which restores everything > >> to working order but also triggers vfio_bar_restore() in the process.... So > >> this isn't the right answer, more of a proof-of-concept. > >> > >> @Alex: Any guidance on what needs to happen to make qemu-s390x happy with this > >> recent kernel change? > > > > Bummer! I won't claim to understand s390 PCI, but if we have a VF > > exposed to the "host" (ie. the first level where vfio-pci is being > > used), but we can't tell that it's a VF, how do we know whether the > > memory bit in the command register is unimplemented because it's a VF > > or unimplemented because the device doesn't support MMIO? How are the > > device ID, vendor ID, and BAR registers virtualized to the host? Could > > the memory enable bit also be emulated by that virtualization, much > > like vfio-pci does for userspace? If the other registers are > > virtualized, but these command register bits are left unimplemented, do > > we need code to deduce that we have a VF based on the existence of MMIO > > BARs, but lack of memory enable bit? Thanks, > > > > Alex > > Alex, Matt, > > in s390 we have the possibility to assign a virtual function to a > logical partition as function 0. > In this case it can not be treated as a virtual function but must be > treated as a physical function. > This is currently working very well. > However, these functions do not set PCI_COMMAND_MEMORY as we need. Where is the vendor and device ID virtualization done for these devices, we can't have a PF with IDs 0000:0000. > Shouldn't we fix this inside the kernel, to keep older QMEU working? > > Then would it be OK to add a new bit/boolean inside the > pci_dev/vfio_pci_device like, is_detached_vfn, that we could set during > enumeration and test inside __vfio_pci_memory_enabled() to return true? Probably each instance of is_virtfn in vfio-pci should be looked at to see if it applies to s390. If we're going to recognize this as a VF, I'd rather we complete the emulation that the lower level hypervisor has missed. If we can enable all the is_virtfn code on s390, then we should probably cache is_virtfn on the vfio_pci_device object and allow s390 a place to set it once at probe or enable time. > In the enumeration we have the possibility to know if the function is a > HW/Firmware virtual function on devfn 0 or if it is created by SRIOV. > > It seems an easy fix without side effects. > > What do you think? It sure seems preferable to recognize that it is a VF in the kernel than to require userspace to have arch specific hacks. Thanks, Alex