Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider: - [High] PCI/P2PDMA: missing upstream forwarding check in calc_map_type_and_dist() - [Medium] PCI/P2PDMA: masked redirect and read warnings in calc_map_type_and_dist() --
commit ae19e046716c7bc5dbb292aa22e00859ce94d08e Author: Leon Romanovsky <[email protected]> PCI/P2PDMA: Evaluate ACS controls at the path divergence This commit updates calc_map_type_and_dist() to evaluate ACS directional redirect controls at the path divergence rather than below it. It also checks for internal routes between functions sharing a PCIe link, verifies ACS Upstream Forwarding on shared downstream ports, and rejects unreadable ACS Control registers. > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index dbab955dcbdbb..8ca0c9ba87c23 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -589,6 +590,65 @@ static bool pci_acs_p2pdma_ctrl(struct pci_dev *pdev, > u16 *ctrl) [ ... ] > +static struct pci_dev * > +pci_acs_p2pdma_no_upstream_forwarding(struct pci_dev *common) > +{ > + struct pci_dev *pdev; > + u16 ctrl; > + > + for (pdev = common; pdev; pdev = pci_upstream_bridge(pdev)) { > + if (!pci_acs_p2pdma_downstream_port(pdev)) > + continue; > + > + if (!pci_acs_p2pdma_ctrl(pdev, &ctrl)) > + return pdev; > + > + /* > + * Include Root Ports here. The PCIe port type check excludes > + * the legacy AMD southbridge quirk, which may sleep. > + */ > + if (pci_dev_specific_acs_enabled(pdev, PCI_ACS_UF) > 0) > + continue; > + > + if (!(pdev->acs_cap && pdev->acs_capabilities & ctrl & > PCI_ACS_UF)) > + return pdev; > + } > + > + return NULL; > +} [ ... ] > @@ -865,57 +932,106 @@ calc_map_type_and_dist(struct pci_dev *provider, > struct pci_dev *client, [ ... ] > +check_paths_acs: > + *dist = dist_a + dist_b; > > + /* > + * ACS P2P routing controls apply where a TLP can route toward the peer > + * or upstream. Below that divergence, its only route toward the other > + * branch is upstream, so redirect controls do not affect the path. > + */ > + if (a_child && b_child) { > + if (pci_acs_p2pdma_ctrl(a_child, &ctrl)) > + state = pci_acs_p2pdma_completion(ctrl); > + if (state != PCI_ACS_P2PDMA_DIRECT) { > + pci_p2pdma_list_redir(&acs_list, &quirk_list, a_child); > + if (state == PCI_ACS_P2PDMA_REDIRECT) > + acs_redirect_cnt++; > + else if (!acs_unreadable) > + acs_unreadable = a_child; > + } > > + state = PCI_ACS_P2PDMA_NOT_SUPPORTED; > + if (pci_acs_p2pdma_ctrl(b_child, &ctrl)) > + state = pci_acs_p2pdma_request(ctrl); > + if (state != PCI_ACS_P2PDMA_DIRECT) { > + pci_p2pdma_list_redir(&acs_list, &quirk_list, b_child); > + if (state == PCI_ACS_P2PDMA_REDIRECT) > + acs_redirect_cnt++; > + else if (!acs_unreadable) > + acs_unreadable = b_child; > + } > + /* > + * Two children of one Downstream or Root Port share a link. > + * Use topology rather than slot numbers or the multifunction > + * bit, since ARI functions and VFs need not share those. > + */ > + if (pci_acs_p2pdma_downstream_port(a)) { > + req_upstream = > + pci_acs_p2pdma_no_internal_route(b_child, > PCI_ACS_RR); > + cpl_upstream = > + pci_acs_p2pdma_no_internal_route(a_child, > PCI_ACS_CR); > + uf_blocked = pci_acs_p2pdma_no_upstream_forwarding(a); > + } > } [Severity: High] When provider and client sit behind different Switch Downstream Ports of a PCIe Switch, their lowest common ancestor a in calc_map_type_and_dist() is the Switch Upstream Port (PCI_EXP_TYPE_UPSTREAM), where pci_acs_p2pdma_downstream_port(a) is false. If b_child has PCI_ACS_RR or PCI_ACS_EC enabled, or a_child has PCI_ACS_CR enabled, the switch redirects traffic upstream out of the Switch Upstream Port a toward the host bridge. That redirected TLP then arrives on the secondary interface of every shared Switch Downstream Port (in a cascaded switch topology) and Root Port above a with its target also behind that same secondary interface, requiring PCI_ACS_UF on those shared ports to reach the host bridge. Although pci_acs_p2pdma_no_upstream_forwarding() already walks up pci_upstream_bridge() while skipping Switch Upstream Ports, calling it only inside if (pci_acs_p2pdma_downstream_port(a)) skips checking the shared Downstream and Root Ports above a when a is a Switch Upstream Port. Can this cause calc_map_type_and_dist() to return PCI_P2PDMA_MAP_THRU_HOST_BRIDGE instead of PCI_P2PDMA_MAP_NOT_SUPPORTED when an ancestor port above the switch lacks PCI_ACS_UF or has an unreadable ACS Control register? > + /* > + * Below a shared upstream bridge, a path whose divergence ports do not > + * redirect routes the request directly. > + */ > + if (!acs_unreadable && !acs_redirect_cnt && > + !req_upstream && !cpl_upstream) { > map_type = PCI_P2PDMA_MAP_BUS_ADDR; > goto done; > } > > + if (verbose) { > + if (acs_unreadable) > + pci_warn(client, "ACS Control is unreadable for > provider %s at %s\n", > + pci_name(provider), pci_name(acs_unreadable)); > + else if (uf_blocked) > + pci_warn(client, > + "cannot forward peer-to-peer DMA for provider > %s upstream at %s\n", > + pci_name(provider), pci_name(uf_blocked)); > + else if (req_upstream || cpl_upstream) > + pci_warn(client, > + "peer-to-peer DMA with provider %s requires > the host bridge; no internal route between functions\n", > + pci_name(provider)); > + else > + pci_p2pdma_warn_redir(client, provider, &acs_list, > + &quirk_list); > + } [Severity: Medium] How are diagnostics handled here when sibling functions under a Downstream Port or Root Port a DO support internal peer-to-peer routing (!req_upstream && !cpl_upstream), but have PCI_ACS_RR, PCI_ACS_EC, or PCI_ACS_CR enabled on the functions themselves (acs_redirect_cnt > 0)? In that case, disabling ACS redirect on the functions via pci=disable_acs_redir= would allow them to use their internal route (PCI_P2PDMA_MAP_BUS_ADDR) without traversing port a. However, because uf_blocked = pci_acs_p2pdma_no_upstream_forwarding(a) is evaluated unconditionally and checked before the final else branch in the verbose block, if port a or an ancestor port does not have PCI_ACS_UF enabled, calc_map_type_and_dist() only warns about upstream forwarding at uf_blocked and suppresses pci_p2pdma_warn_redir(). Additionally, pci_acs_p2pdma_no_upstream_forwarding() is called before the PCI_P2PDMA_MAP_BUS_ADDR check (reading PCI_ACS_CTRL up the hierarchy even when the functions route directly), and when pci_acs_p2pdma_ctrl() fails on an upstream port, it returns that port as uf_blocked rather than acs_unreadable, logging an upstream-forwarding message instead of an unreadable ACS Control warning. Should pci_acs_p2pdma_no_upstream_forwarding() only be evaluated after the direct-route check, distinguish unreadable ACS Control registers from missing PCI_ACS_UF, and still emit pci_p2pdma_warn_redir() when programmable redirect bits blocked a valid direct route? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=5
