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

[Darrel Goeddel]

On 5/28/20 4:38 PM, Alex Williamson wrote:
> On Thu, 28 May 2020 13:57:42 -0700
> Ashok Raj <ashok.raj@xxxxxxxxx> 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:
> > â 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).
> > â 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.
> > â 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@xxxxxxxxxxxxxxxx  I'd drop that tag, that's my nit.
> Otherwise:
>
> Reviewed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>

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@xxxxxxxxxxxxxx>

> > Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> > To: Joerg Roedel <joro@xxxxxxxxxx>
> > To: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > Cc: Darrel Goeddel <DGoeddel@xxxxxxxxxxxxxx>
> > Cc: Mark Scott <mscott@xxxxxxxxxxxxxx>,
> > Cc: Romil Sharma <rsharma@xxxxxxxxxxxxxx>
> > Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
> > ---
> > 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 },