Re: [PATCH V10 6/8] PCI/P2PDMA: Add a 10-Bit Tag check in P2PDMA
flat view
From: Bjorn Helgaas <helgaas@kernel.org>
Date: 2021-10-27 21:21:54
Also in:
linux-media, linux-pci
On Sat, Oct 09, 2021 at 06:49:36PM +0800, Dongdong Liu wrote:
Add a 10-Bit Tag check in the P2PDMA code to ensure that a device with 10-Bit Tag Requester doesn't interact with a device that does not support 10-Bit Tag Completer.
Shouldn't this also take into account Extended Tags (8 bits)? I think the only tag size guaranteed to be supported is 5 bits.
Before that happens, the kernel should emit a warning.
The warning is nice, but the critical thing is that the P2PDMA mapping should fail so we don't attempt DMA in this situation. I guess that's sort of what you're saying with "ensure that a device ... doesn't interact with a device ..."
quoted hunk ↗ jump to hunk
"echo 0 > /sys/bus/pci/devices/.../10bit_tag" to disable 10-Bit Tag Requester for PF device. "echo 0 > /sys/bus/pci/devices/.../sriov_vf_10bit_tag_ctl" to disable 10-Bit Tag Requester for VF device. Signed-off-by: Dongdong Liu <redacted> Reviewed-by: Logan Gunthorpe <logang@deltatee.com> --- drivers/pci/p2pdma.c | 48 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+)diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index 50cdde3e9a8b..804e390f4c22 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c@@ -19,6 +19,7 @@ #include <linux/random.h> #include <linux/seq_buf.h> #include <linux/xarray.h> +#include "pci.h" enum pci_p2pdma_map_type { PCI_P2PDMA_MAP_UNKNOWN = 0,@@ -410,6 +411,50 @@ static unsigned long map_types_idx(struct pci_dev *client) (client->bus->number << 8) | client->devfn; } +static bool pci_10bit_tags_unsupported(struct pci_dev *a, + struct pci_dev *b, + bool verbose) +{ + bool req; + bool comp; + u16 ctl; + const char *str = "10bit_tag"; + + if (a->is_virtfn) { +#ifdef CONFIG_PCI_IOV + req = !!(a->physfn->sriov->ctrl & + PCI_SRIOV_CTRL_VF_10BIT_TAG_REQ_EN); +#endif + } else { + pcie_capability_read_word(a, PCI_EXP_DEVCTL2, &ctl); + req = !!(ctl & PCI_EXP_DEVCTL2_10BIT_TAG_REQ_EN); + } + + comp = !!(b->devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP); + /* 10-bit tags not enabled on requester */ + if (!req) + return false; + + /* Completer can handle anything */ + if (comp) + return false; + + if (!verbose) + return true; + + pci_warn(a, "cannot be used for peer-to-peer DMA as 10-Bit Tag Requester enable is set for this device, but peer device (%s) does not support the 10-Bit Tag Completer\n", + pci_name(b)); + + if (a->is_virtfn) + str = "sriov_vf_10bit_tag_ctl"; + + pci_warn(a, "to disable 10-Bit Tag Requester for this device, echo 0 > /sys/bus/pci/devices/%s/%s\n", + pci_name(a), str); + + return true; +} + /* * Calculate the P2PDMA mapping type and distance between two PCI devices. *@@ -532,6 +577,9 @@ calc_map_type_and_dist(struct pci_dev *provider, struct pci_dev *client, map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED; } done: + if (pci_10bit_tags_unsupported(client, provider, verbose)) + map_type = PCI_P2PDMA_MAP_NOT_SUPPORTED; + rcu_read_lock(); p2pdma = rcu_dereference(provider->p2pdma); if (p2pdma)-- 2.22.0