linux-kernel - Re: [PATCH v11 04/13] PCI: Allow PASID only when ACS enforced on upstreaming path

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Date:   Tue, 23 Aug 2022 15:10:00 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 04/13] PCI: Allow PASID only when ACS enforced on
 upstreaming path

On 2022/8/18 21:04, Jason Gunthorpe wrote:
> On Wed, Aug 17, 2022 at 09:20:15AM +0800, Lu Baolu wrote:
>> Some configurations of the PCI fabric will route device originated TLP
>> packets based on the memory addresses. These configurations are
>> incompatible with PASID as the PASID packets form a distinct address
>> space. For instance, any configuration where switches are present
>> without ACS enabled is incompatible.
>>
>> This enhances the pci_enable_pasid() interface by requiring the ACS to
>> support Source Validation, Request Redirection, Completer Redirection,
>> and Upstream Forwarding. This effectively means that devices cannot
>> spoof their requester ID, requests and completions cannot be redirected,
>> and all transactions are forwarded upstream, even as it passes through a
>> bridge where the target device is downstream.
>>
>> Suggested-by: Jason Gunthorpe<jgg@...dia.com>
>> Suggested-by: Kevin Tian<kevin.tian@...el.com>
>> Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
>> ---
>>   drivers/pci/ats.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
>> index c967ad6e2626..0715e48e7973 100644
>> --- a/drivers/pci/ats.c
>> +++ b/drivers/pci/ats.c
>> @@ -382,6 +382,11 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
>>   	if (!pasid)
>>   		return -EINVAL;
>>   
>> +	if (!pci_acs_path_enabled(pdev, NULL,
>> +				  PCI_ACS_SV | PCI_ACS_RR |
>> +				  PCI_ACS_CR | PCI_ACS_UF))
> I think we only need RR and UF here?
> 
> Source Validation causes the switch to validate the requestor RID in
> each TLP which has nothing to do with address based routing
> 
> Completion Redirect changes how RID routing works, and has nothing to
> do with address based routing.
> 
> Yes, both of those are usually set for virtualization scenarios but we
> shouldn't check it here as a basic requirement to enable PASID.

Yes. Here only requires RR and UF.

Best regards,
baolu