From: Bjorn Helgaas <helgaas@kernel.org>
To: Baolu Lu <baolu.lu@linux.intel.com>
Cc: "Bjorn Helgaas" <bhelgaas@google.com>,
"Joerg Roedel" <jroedel@suse.de>,
"Matt Fagnani" <matt.fagnani@bell.net>,
"Christian König" <christian.koenig@amd.com>,
"Jason Gunthorpe" <jgg@nvidia.com>,
"Kevin Tian" <kevin.tian@intel.com>,
"Vasant Hegde" <vasant.hegde@amd.com>,
"Tony Zhu" <tony.zhu@intel.com>,
linux-pci@vger.kernel.org, iommu@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/1] PCI: Add translated request only flag for pci_enable_pasid()
Date: Thu, 2 Feb 2023 14:12:49 -0600 [thread overview]
Message-ID: <20230202201249.GA1963053@bhelgaas> (raw)
In-Reply-To: <b75a5a94-a962-f88e-149e-7d23982a7ad2@linux.intel.com>
[Joerg, you may be able to answer this. Patch under discussion is:
https://lore.kernel.org/r/20230114073420.759989-1-baolu.lu@linux.intel.com]
On Thu, Feb 02, 2023 at 11:08:25AM +0800, Baolu Lu wrote:
> ...
> ACS is unnecessary for the devices that only use translated memory request
> for PASID. All translated addresses are granted by the Linux kernel which
> ensures that such addresses will never be in a P2P address, i.e., it's not
> contained in any bridge aperture, will *always* be routed toward the RC.
Re 201007ef707a ("PCI: Enable PASID only when ACS RR & UF enabled on
upstream path"), does that commit actually *fix* anything? I wonder
whether we could revert it completely.
The intent of 201007ef707a is to use ACS to prevent misrouting, which
would happen if a TLP contained an address that *looked* like a PCI
bus address, i.e., it was inside a host bridge aperture, but was
*intended* to reach an IOMMU or main memory directly.
201007ef707a only affects pci_enable_pasid(), so I think we already
avoid this misrouting by restricting DMA address allocation for both
non-IOMMU scenarios and non-PASID IOMMU scenarios.
So what about PASID mappings, e.g., consider a mapping of (Requester
ID, PASID, Untranslated Address) -> Translated Address? If either the
Untranslated Address or the Translated Address looks like a PCI bus
address, a Memory Request or Translation Request could be misrouted.
Does that actually happen? I assume it does not happen for Translated
Addresses because that's basically the non-IOMMU case, and we don't
need ACS to prevent misrouting there.
Do IOMMUs allocate (PASID, Untranslated Addresses) that look like PCI
bus addresses?
Bjorn
next prev parent reply other threads:[~2023-02-02 20:12 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-14 7:34 [PATCH v3 1/1] PCI: Add translated request only flag for pci_enable_pasid() Lu Baolu
2023-01-16 15:42 ` Jason Gunthorpe
2023-01-27 11:30 ` Linux kernel regression tracking (Thorsten Leemhuis)
2023-01-27 17:30 ` Bjorn Helgaas
2023-01-28 7:52 ` Tian, Kevin
2023-01-29 8:42 ` Baolu Lu
2023-01-30 18:38 ` Bjorn Helgaas
2023-01-30 18:47 ` Jason Gunthorpe
2023-01-31 23:50 ` Bjorn Helgaas
2023-02-01 2:28 ` Jason Gunthorpe
2023-01-31 12:25 ` Baolu Lu
2023-02-01 16:58 ` Bjorn Helgaas
2023-02-02 3:08 ` Baolu Lu
2023-02-02 20:12 ` Bjorn Helgaas [this message]
2023-02-02 20:45 ` Jason Gunthorpe
2023-02-03 18:20 ` Bjorn Helgaas
2023-02-03 18:52 ` Jason Gunthorpe
2023-02-06 4:28 ` Tian, Kevin
2023-01-31 12:56 ` Baolu Lu
2023-02-01 0:14 ` Bjorn Helgaas
2023-02-01 2:36 ` Jason Gunthorpe
2023-02-01 14:09 ` Jonathan Cameron
2023-02-01 5:18 ` Vasant Hegde
2023-02-01 5:51 ` Baolu Lu
2023-02-01 5:59 ` Baolu Lu
2023-02-01 6:31 ` Baolu Lu
2023-02-01 14:22 ` Jason Gunthorpe
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