From: Bjorn Helgaas <helgaas@kernel.org> To: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, ashok.raj@intel.com, keith.busch@intel.com, Joerg Roedel <joro@8bytes.org>, David Woodhouse <dwmw2@infradead.org>, iommu@lists.linux-foundation.org Subject: Re: [PATCH v5 4/7] PCI/ATS: Add PRI support for PCIe VF devices Date: Mon, 19 Aug 2019 09:15:00 -0500 Message-ID: <20190819141500.GQ253360@google.com> (raw) In-Reply-To: <f05eb779-9f78-f20f-7626-16b8bd28af40@linux.intel.com> On Thu, Aug 15, 2019 at 03:39:03PM -0700, Kuppuswamy Sathyanarayanan wrote: > On 8/15/19 3:20 PM, Bjorn Helgaas wrote: > > [+cc Joerg, David, iommu list: because IOMMU drivers are the only > > callers of pci_enable_pri() and pci_enable_pasid()] > > > > On Thu, Aug 01, 2019 at 05:06:01PM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote: > > > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> > > > > > > When IOMMU tries to enable Page Request Interface (PRI) for VF device > > > in iommu_enable_dev_iotlb(), it always fails because PRI support for > > > PCIe VF device is currently broken. Current implementation expects > > > the given PCIe device (PF & VF) to implement PRI capability before > > > enabling the PRI support. But this assumption is incorrect. As per PCIe > > > spec r4.0, sec 9.3.7.11, all VFs associated with PF can only use the > > > PRI of the PF and not implement it. Hence we need to create exception > > > for handling the PRI support for PCIe VF device. > > > > > > Also, since PRI is a shared resource between PF/VF, following rules > > > should apply. > > > > > > 1. Use proper locking before accessing/modifying PF resources in VF > > > PRI enable/disable call. > > > 2. Use reference count logic to track the usage of PRI resource. > > > 3. Disable PRI only if the PRI reference count (pri_ref_cnt) is zero. > > Wait, why do we need this at all? I agree the spec says VFs may not > > implement PRI or PASID capabilities and that VFs use the PRI and > > PASID of the PF. > > > > But why do we need to support pci_enable_pri() and pci_enable_pasid() > > for VFs? There's nothing interesting we can *do* in the VF, and > > passing it off to the PF adds all this locking mess. For VFs, can we > > just make them do nothing or return -EINVAL? What functionality would > > we be missing if we did that? > > Currently PRI/PASID capabilities are not enabled by default. IOMMU can > enable PRI/PASID for VF first (and not enable it for PF). In this case, > doing nothing for VF device will break the functionality. What is the path where we can enable PRI/PASID for VF but not for the PF? The call chains leading to pci_enable_pri() go through the iommu_ops.add_device interface, which makes me think this is part of the device enumeration done by the PCI core, and in that case I would think this it should be done for the PF before VFs. But maybe this path isn't exercised until a driver does a DMA map or something similar? Bjorn
next prev parent reply index Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-02 0:05 [PATCH v5 0/7] Fix PF/VF dependency issue sathyanarayanan.kuppuswamy 2019-08-02 0:05 ` [PATCH v5 1/7] PCI/ATS: Fix pci_prg_resp_pasid_required() dependency issues sathyanarayanan.kuppuswamy 2019-08-12 20:04 ` Bjorn Helgaas 2019-08-12 20:20 ` sathyanarayanan kuppuswamy 2019-08-13 3:51 ` Bjorn Helgaas 2019-08-16 18:06 ` Kuppuswamy Sathyanarayanan 2019-08-02 0:05 ` [PATCH v5 2/7] PCI/ATS: Initialize PRI in pci_ats_init() sathyanarayanan.kuppuswamy 2019-08-12 20:04 ` Bjorn Helgaas 2019-08-12 21:35 ` sathyanarayanan kuppuswamy 2019-08-13 4:10 ` Bjorn Helgaas 2019-08-15 4:46 ` Bjorn Helgaas 2019-08-15 17:30 ` Kuppuswamy Sathyanarayanan 2019-08-16 17:31 ` Bjorn Helgaas 2019-08-02 0:06 ` [PATCH v5 3/7] PCI/ATS: Initialize PASID " sathyanarayanan.kuppuswamy 2019-08-12 20:04 ` Bjorn Helgaas 2019-08-15 4:48 ` Bjorn Helgaas 2019-08-15 4:56 ` Bjorn Helgaas 2019-08-15 17:31 ` Kuppuswamy Sathyanarayanan 2019-08-02 0:06 ` [PATCH v5 4/7] PCI/ATS: Add PRI support for PCIe VF devices sathyanarayanan.kuppuswamy 2019-08-12 20:04 ` Bjorn Helgaas 2019-08-12 21:40 ` sathyanarayanan kuppuswamy 2019-08-13 4:16 ` Bjorn Helgaas 2019-08-15 22:20 ` Bjorn Helgaas 2019-08-15 22:39 ` Kuppuswamy Sathyanarayanan 2019-08-19 14:15 ` Bjorn Helgaas [this message] 2019-08-19 22:53 ` Kuppuswamy Sathyanarayanan 2019-08-19 23:19 ` Bjorn Helgaas 2019-08-28 18:21 ` Kuppuswamy Sathyanarayanan 2019-08-28 18:57 ` Bjorn Helgaas 2019-08-02 0:06 ` [PATCH v5 5/7] PCI/ATS: Add PASID " sathyanarayanan.kuppuswamy 2019-08-12 20:05 ` Bjorn Helgaas 2019-08-13 22:19 ` Kuppuswamy Sathyanarayanan 2019-08-15 5:04 ` Bjorn Helgaas 2019-08-16 1:21 ` Kuppuswamy Sathyanarayanan 2019-08-02 0:06 ` [PATCH v5 6/7] PCI/ATS: Disable PF/VF ATS service independently sathyanarayanan.kuppuswamy 2019-08-02 0:06 ` [PATCH v5 7/7] PCI: Skip Enhanced Allocation (EA) initialization for VF device sathyanarayanan.kuppuswamy
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20190819141500.GQ253360@google.com \ --to=helgaas@kernel.org \ --cc=ashok.raj@intel.com \ --cc=dwmw2@infradead.org \ --cc=iommu@lists.linux-foundation.org \ --cc=joro@8bytes.org \ --cc=keith.busch@intel.com \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-pci@vger.kernel.org \ --cc=sathyanarayanan.kuppuswamy@linux.intel.com \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-PCI Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-pci/0 linux-pci/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-pci linux-pci/ https://lore.kernel.org/linux-pci \ linux-pci@vger.kernel.org public-inbox-index linux-pci Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-pci AGPL code for this site: git clone https://public-inbox.org/public-inbox.git