Re: Re: [PATCH] PCI: Relax ACS requirement for Intel RCiEP devices.

Darrel Goeddel
2020-05-29T16:14:47Z

On 5/28/20 4:38 PM, Alex Williamson wrote:
> On Thu, 28 May 2020 13:57:42 -0700
> Ashok Raj <ashok.raj@intel.com> wrote:
>
>> All Intel platforms guarantee that all root complex implementations
>> must send transactions up to IOMMU for address translations. Hence for
>> RCiEP devices that are Vendor ID Intel, can claim exception for lack of
>> ACS support.
>>
>>
>> 3.16 Root-Complex Peer to Peer Considerations
>> When DMA remapping is enabled, peer-to-peer requests through the
>> Root-Complex must be handled
>> as follows:
>> • The input address in the request is translated (through first-level,
>> second-level or nested translation) to a host physical address (HPA).
>> The address decoding for peer addresses must be done only on the
>> translated HPA. Hardware implementations are free to further limit
>> peer-to-peer accesses to specific host physical address regions
>> (or to completely disallow peer-forwarding of translated requests).
>> • Since address translation changes the contents (address field) of
>> the PCI Express Transaction Layer Packet (TLP), for PCI Express
>> peer-to-peer requests with ECRC, the Root-Complex hardware must use
>> the new ECRC (re-computed with the translated address) if it
>> decides to forward the TLP as a peer request.
>> • Root-ports, and multi-function root-complex integrated endpoints, may
>> support additional peerto-peer control features by supporting PCI Express
>> Access Control Services (ACS) capability. Refer to ACS capability in
>> PCI Express specifications for details.
>>
>> Since Linux didn't give special treatment to allow this exception, certain
>> RCiEP MFD devices are getting grouped in a single iommu group. This
>> doesn't permit a single device to be assigned to a guest for instance.
>>
>> In one vendor system: Device 14.x were grouped in a single IOMMU group.
>>
>> /sys/kernel/iommu_groups/5/devices/0000:00:14.0
>> /sys/kernel/iommu_groups/5/devices/0000:00:14.2
>> /sys/kernel/iommu_groups/5/devices/0000:00:14.3
>>
>> After the patch:
>> /sys/kernel/iommu_groups/5/devices/0000:00:14.0
>> /sys/kernel/iommu_groups/5/devices/0000:00:14.2
>> /sys/kernel/iommu_groups/6/devices/0000:00:14.3 <<< new group
>>
>> 14.0 and 14.2 are integrated devices, but legacy end points.
>> Whereas 14.3 was a PCIe compliant RCiEP.
>>
>> 00:14.3 Network controller: Intel Corporation Device 9df0 (rev 30)
>> Capabilities: [40] Express (v2) Root Complex Integrated Endpoint, MSI 00
>>
>> This permits assigning this device to a guest VM.
>>
>> Fixes: f096c061f552 ("iommu: Rework iommu_group_get_for_pci_dev()")
>
> I don't really understand this Fixes tag. This seems like a feature,
> not a fix. If you want it in stable releases as a feature, request it
> via Cc: stable@vger.kernel.org. I'd drop that tag, that's my nit.
> Otherwise:
>
> Reviewed-by: Alex Williamson <alex.williamson@redhat.com>

I have tested this patch with 5.6.14 as well as a slightly modified
version (without pci_acs_ctrl_enabled()) in a 3.10 enterprise linux
kernel.

Tested-by: Darrel Goeddel <dgoeddel@forcepoint.com>

>> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
>> To: Joerg Roedel <joro@8bytes.org>
>> To: Bjorn Helgaas <bhelgaas@google.com>
>> Cc: linux-kernel@vger.kernel.org
>> Cc: iommu@lists.linux-foundation.org
>> Cc: Lu Baolu <baolu.lu@linux.intel.com>
>> Cc: Alex Williamson <alex.williamson@redhat.com>
>> Cc: Darrel Goeddel <DGoeddel@forcepoint.com>
>> Cc: Mark Scott <mscott@forcepoint.com>,
>> Cc: Romil Sharma <rsharma@forcepoint.com>
>> Cc: Ashok Raj <ashok.raj@intel.com>
>> ---
>> v2: Moved functionality from iommu to pci quirks - Alex Williamson
>>
>> drivers/pci/quirks.c | 15 +++++++++++++++
>> 1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
>> index 28c9a2409c50..63373ca0a3fe 100644
>> --- a/drivers/pci/quirks.c
>> +++ b/drivers/pci/quirks.c
>> @@ -4682,6 +4682,20 @@ static int pci_quirk_mf_endpoint_acs(struct pci_dev *dev, u16 acs_flags)
>> PCI_ACS_CR | PCI_ACS_UF | PCI_ACS_DT);
>> }
>>
>> +static int pci_quirk_rciep_acs(struct pci_dev *dev, u16 acs_flags)
>> +{
>> + /*
>> + * RCiEP's are required to allow p2p only on translated addresses.
>> + * Refer to Intel VT-d specification Section 3.16 Root-Complex Peer
>> + * to Peer Considerations
>> + */
>> + if (pci_pcie_type(dev) != PCI_EXP_TYPE_RC_END)
>> + return -ENOTTY;
>> +
>> + return pci_acs_ctrl_enabled(acs_flags,
>> + PCI_ACS_SV | PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF);
>> +}
>> +
>> static int pci_quirk_brcm_acs(struct pci_dev *dev, u16 acs_flags)
>> {
>> /*
>> @@ -4764,6 +4778,7 @@ static const struct pci_dev_acs_enabled {
>> /* I219 */
>> { PCI_VENDOR_ID_INTEL, 0x15b7, pci_quirk_mf_endpoint_acs },
>> { PCI_VENDOR_ID_INTEL, 0x15b8, pci_quirk_mf_endpoint_acs },
>> + { PCI_VENDOR_ID_INTEL, PCI_ANY_ID, pci_quirk_rciep_acs },
>> /* QCOM QDF2xxx root ports */
>> { PCI_VENDOR_ID_QCOM, 0x0400, pci_quirk_qcom_rp_acs },
>> { PCI_VENDOR_ID_QCOM, 0x0401, pci_quirk_qcom_rp_acs },
>