Re: [PATCH] PCI: revert "Enable PASID only when ACS RR & UF enabled on upstream path"

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Forgot to add Felix as CC as well.

Am 11.01.23 um 09:57 schrieb Christian König:
> This reverts commit 201007ef707a8bb5592cd07dd46fc9222c48e0b9.
>
> It's correct that the PCIe fabric routes Memory Requests based on the
> TLP address, but enabling the PASID mapping doesn't necessary mean that
> Memory Requests will have a PASID associated with them.
>
> The alternative is ATS which lets the device resolve the PASID+addr pair
> before a memory request is made into a routeable TLB address through the
> TA. Those resolved addresses are then cached on the device instead of
> in the IOMMU TLB.
>
> So the assumption that you mandatory need ACS to enabled PASID handling
> on a device is simply not correct, we need to take ATS into account as
> well.
>
> The patch caused failures with AMDs integrated GPUs because some of them
> only enable ATS but not ACS.
>
> For now just revert the patch until this is completely solved.
>
> CC: Jason Gunthorpe <jgg@nvidia.com>
> CC: Kevin Tian <kevin.tian@intel.com>
> CC: Lu Baolu <baolu.lu@linux.intel.com>
> CC: Bjorn Helgaas <bhelgaas@google.com>
> CC: Tony Zhu <tony.zhu@intel.com>
> CC: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> Bug: https://bugzilla.kernel.org/show_bug.cgi?id=216865
> ---
>   drivers/pci/ats.c | 3 ---
>   1 file changed, 3 deletions(-)
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index f9cc2e10b676..c967ad6e2626 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -382,9 +382,6 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
>   	if (!pasid)
>   		return -EINVAL;
>   
> -	if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
> -		return -EINVAL;
> -
>   	pci_read_config_word(pdev, pasid + PCI_PASID_CAP, &supported);
>   	supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
>