linux-kernel - Re: [PATCH v2 1/3] iommu: Make single-device group for PASID explicit

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Date:   Mon, 21 Aug 2023 13:44:33 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Nicolin Chen <nicolinc@...dia.com>
Cc:     baolu.lu@...ux.intel.com, "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] iommu: Make single-device group for PASID explicit

On 2023/8/18 11:56, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Monday, August 14, 2023 9:18 AM
>>
>> The PASID interfaces have always supported only single-device groups.
>> This was first introduced in commit 26b25a2b98e45 ("iommu: Bind process
>> address spaces to devices"), and has been kept consistent in subsequent
>> commits.
>>
>> However, the core code doesn't explicitly check for this requirement
>> after commit 201007ef707a8 ("PCI: Enable PASID only when ACS RR & UF
>> enabled on upstream path"), which made this requirement implicit.
>>
>> Restore the check to make it explicit that the PASID interfaces only
>> support devices belonging to single-device groups.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> ---
>>   drivers/iommu/iommu.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 71b9c41f2a9e..f1eba60e573f 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -3408,6 +3408,11 @@ int iommu_attach_device_pasid(struct
>> iommu_domain *domain,
>>   		return -ENODEV;
>>
>>   	mutex_lock(&group->mutex);
>> +	if (list_count_nodes(&group->devices) != 1) {
>> +		ret = -EINVAL;
>> +		goto out_unlock;
>> +	}
>> +
> 
> I wonder whether we should also block adding new device to this
> group once the single-device has pasid enabled. Otherwise the

This has been guaranteed by pci_enable_pasid():

         if (!pci_acs_path_enabled(pdev, NULL, PCI_ACS_RR | PCI_ACS_UF))
                 return -EINVAL;

> check alone at attach time doesn't mean this group won't be
> expanded to have multiple devices later.

Best regards,
baolu