Messages in this thread | | | Date | Wed, 6 Apr 2022 19:03:12 +0800 | Subject | Re: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown() | From | Lu Baolu <> |
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On 2022/4/6 18:44, Tian, Kevin wrote: >> 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.
Yes! You are right.
> >> >> /* 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;
If !pdev->multifunction, do we still need to start from the device itself? ACS is only for MFDs and bridges, do I understand it right? Do we need to consider the SRIOV case?
> >> >> /* 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.
Okay! Thanks!
> Thanks > Kevin
Best regards, baolu
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