On Sat, Jan 14, 2023 at 03:34:20PM +0800, Lu Baolu wrote:
> The PCIe fabric routes Memory Requests based on the TLP address, ignoring
> the PASID. In order to ensure system integrity, commit 201007ef707a ("PCI:
> Enable PASID only when ACS RR & UF enabled on upstream path") requires
> some ACS features being supported on device's upstream path when enabling
> PCI/PASID.
>
> One alternative is ATS/PRI which lets the device resolve the PASID + addr
> pair before a memory request is made into a routeable TLB address through
> the translation agent.
This sounds like "ATS/PRI" is a solution to a problem, but we haven't
stated the problem yet.
> Those resolved addresses are then cached on the
> device instead of in the IOMMU TLB and the device always sets translated
> bit for PASID. One example of those devices are AMD graphic devices that
> always have ACS or ATS/PRI enabled together with PASID.
>
> This adds a flag parameter in the pci_enable_pasid() helper, with which
> the device driver could opt-in the fact that device always sets the
> translated bit for PASID.
Nit: "Add a flag ..." and "Apply this opt-in ..." (below).
> It also applies this opt-in for AMD graphic devices. Without this change,
> kernel boots to black screen on a system with below AMD graphic device:
>
> 00:01.0 VGA compatible controller: Advanced Micro Devices, Inc.
> [AMD/ATI] Wani [Radeon R5/R6/R7 Graphics] (rev ca)
> (prog-if 00 [VGA controller])
> DeviceName: ATI EG BROADWAY
> Subsystem: Hewlett-Packard Company Device 8332
What is the underlying failure here? "Black screen" is useful but we
should say *why* that happens, e.g., transactions went the wrong place
or whatever.
> At present, it is a common practice to enable/disable PCI PASID in the
> iommu drivers. Considering that the device driver knows more about the
> specific device, we will follow up by moving pci_enable_pasid() into
> the specific device drivers.
> @@ -353,12 +353,15 @@ void pci_pasid_init(struct pci_dev *pdev)
> * pci_enable_pasid - Enable the PASID capability
> * @pdev: PCI device structure
> * @features: Features to enable
> + * @flags: device-specific flags
> + * - PCI_PASID_XLATED_REQ_ONLY: The PCI device always use translated type
> + * for all PASID memory requests.
s/use/uses/
I guess PCI_PASID_XLATED_REQ_ONLY is something only the driver knows,
right? We can't deduce from architected config space that the device
will produce PASID prefixes for every Memory Request, can we?
Bjorn
