Messages in this thread | | | From | "Tian, Kevin" <> | Subject | RE: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown() | Date | Wed, 6 Apr 2022 10:44:54 +0000 |
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> From: Lu Baolu <baolu.lu@linux.intel.com> > Sent: Wednesday, April 6, 2022 6:02 PM > > Hi Kevin, > > On 2022/4/2 15:12, Tian, Kevin wrote: > >>>> Add a flag to the group that positively indicates the group can never > >>>> have more than one member, even after hot plug. eg because it is > >>>> impossible due to ACS, or lack of bridges, and so on. > >>> OK, I see your point. It essentially refers to a singleton group which > >>> is immutable to hotplug. > >> Yes, known at creation time, not retroactively enforced because > >> someone used SVA > >> > > We may check following conditions to set the immutable flag when > > a new group is created for a device in pci_device_group(): > > > > 1) ACS is enabled in the upstream path of the device; > > 2) the device is single function or ACS is enabled on a multi-function device; > > 3) the device type is PCI_EXP_TYPE_ENDPOINT (thus no hotplug); > > 4) no 'dma aliasing' on this device; > > > > The last one is a bit conservative as it also precludes a device which aliasing > > dma due to quirks from being treated as a singleton group. But doing so > > saves the effort on trying to separate different aliasing scenarios as defined > > in pci_for_each_dma_alias(). Probably we can go this way as the first step. > > > > Once the flag is set on a group no other event can change it. If a new > > identified device hits an existing singleton group in pci_device_group() > > then it's a bug. > > How about below implementation? > > /* callback for pci_for_each_dma_alias() */ > static int has_pci_alias(struct pci_dev *pdev, u16 alias, void *opaque) > { > return -EEXIST; > } > > static bool pci_dev_is_immutably_isolated(struct pci_dev *pdev) > { > /* Skip bridges. */ > if (pci_is_bridge(pdev)) > return false; > > /* Either connect to root bridge or the ACS-enabled bridge. */ > if (!pci_is_root_bus(pdev->bus) && > !pci_acs_enabled(pdev->bus->self, REQ_ACS_FLAGS)) > return false;
it's not sufficient to just check the non-root bridge itself. This needs to cover the entire path from the bridge to the root port, as pci_device_group() does.
> > /* ACS is required for MFD. */ > if (pdev->multifunction && !pci_acs_enabled(pdev, REQ_ACS_FLAGS)) > return false;
Above two checks be replaced by a simple check as below:
if (!pci_acs_path_enabled(pdev, NULL, REQ_ACS_FLAGS)) return false;
> > /* Make sure no PCI alias. */ > if (pci_for_each_dma_alias(pdev, has_pci_alias, NULL)) > return false; > > return true; > } > > I didn't get why do we need to check the PCI_EXP_TYPE_ENDPOINT device > type. Can you please elaborate a bit more? >
I didn't know there is a pci_is_bridge() facility thus be conservative to restrict it to only endpoint device. If checking pci_is_bridge() alone excludes any hotplug possibility, then it's definitely better.
Thanks Kevin
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