Re: [PATCH v10 17/18] PCI/P2PDMA: Evaluate the ATS path for clients with ATS enabled

[Leon Romanovsky <leon@kernel.org>]

On Mon, Oct 12, 2026 at 01:27:12PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] pci: pci_p2pdma_distance_many() evaluates compatibility without applying client ATS constraints
> --
> 
> commit 254b102fe424913edc3d5f94f8d41bc5d0de2b20
> Author: Leon Romanovsky <leon@kernel.org>
> 
> PCI/P2PDMA: Evaluate the ATS path for clients with ATS enabled
> 
> P2PDMA assumes every client issues Untranslated Requests. A device with
> ATS enabled may translate any address it is handed, including a bus
> address, and Translation Blocking can reject its Translated Requests on
> a route the Untranslated answer called usable.
> 
> > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> > index e38081f797611..a5fc622e3114f 100644
> > --- a/drivers/pci/p2pdma.c
> > +++ b/drivers/pci/p2pdma.c
> 
> [ ... ]
> 
> > @@ -1660,10 +1706,10 @@ pci_p2pdma_map_type_tlp(struct p2pdma_provider *provider, struct device *dev,
> >  		 pci_p2pdma_map_type_name(type), type, provider_state);
> >  
> >  	if (type == PCI_P2PDMA_MAP_UNKNOWN)
> > -		return calc_map_type_and_dist(pdev, client, &dist, tlp_flags,
> > +		type = calc_map_type_and_dist(pdev, client, &dist, tlp_flags,
> >  					      true);
> >  
> > -	return type;
> > +	return pci_p2pdma_client_map_type(pdev, client, per_mapping, type);
> >  }
> 
> [Severity: High]
> Does pci_p2pdma_distance_many() also need to apply these new ATS constraints?
> 
> While this patch successfully updates pci_p2pdma_map_type_tlp() to evaluate ATS
> routing constraints for P2PDMA clients, pci_p2pdma_distance_many() continues
> to evaluate mapping compatibility without them:
> 
> drivers/pci/p2pdma.c:pci_p2pdma_distance_many() {
>     ...
> 		pci_client = find_parent_pci_dev(clients[i]);
> 		if (!pci_client) {
>     ...
> 		map = calc_map_type_and_dist(provider, pci_client, &distance, 0,
> 					     verbose);
>     ...
> }
> 
> If a client has ATS enabled and its Untranslated route is usable but its
> Translated route is blocked by Translation Blocking (or lacks a whitelisted
> host bridge), pci_p2pdma_distance_many() evaluates the Untranslated mapping
> with tlp_flags=0, and incorrectly returns success. 
> 
> When the driver subsequently attempts to map memory, the ATS-aware mapping
> logic will return PCI_P2PDMA_MAP_NOT_SUPPORTED and fail unexpectedly at
> runtime, breaking the API contract of the distance validation.

Yes, Sashiko is right, I'll send new version :(.

Thanks

> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20261012-fix-p2p-acs-v4-0-v10-0-6ffe7b7a4517@nvidia.com?part=17