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SubjectRe: [PATCH v2 0/9] iommu/vt-d: Improve PASID id and table management
From
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Hi,

On 05/16/2018 04:56 PM, Tian, Kevin wrote:
>> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
>> Sent: Wednesday, May 16, 2018 4:01 PM
>>
>> Hi Joerg,
>>
>> Thank you for looking at my patches.
>>
>> On 05/15/2018 10:11 PM, Joerg Roedel wrote:
>>> On Fri, May 04, 2018 at 09:41:15AM +0800, Lu Baolu wrote:
>>>> PATCH 4~9 implement per domain PASID table. Current per IOMMU
>>>> PASID table implementation is insecure in the cases where
>>>> multiple devices under one single IOMMU unit support PASID
>>>> feature. With per domain PASID table, we can achieve finer
>>>> protection and isolation granularity.
>>> Hold on, we hat discussions in the past about doing a system-wide pasid
>>> space, so that every mm_struct with devices attached gets the same pasid
>>> across all devices it is talking to. Reason was that some devices (will)
>>> require this to work correctly. This goes into the opposite direction,
>>> so I am a bit confused here. Please explain, is this not longer
>>> necessary?
>> You are right. System-wide pasid space is necessary, hence PATCH
>> 1~3 implement it. But PATCH 4~9 don't go into the opposite direction,
>> it's designed to address another potential issue.
> one thing you may want to highlight is, even with PATCH 4-9 it's
> still doing system-wide PASID space allocation. Just PASID table
> itself is kept per-device for isolation purpose as you described
> below, i.e. each device can access only those PASIDs which are
> allocated to itself while the allocation happens system-wide...

Yes, exactly.

Best regards,
Lu Baolu

>
>> With system-wide pasid space, we can use a system-wide pasid table,
>> or just keep what we have now(per iommu unit pasid table). Both
>> system-wide and per iommu unitpasid table mean that two devices
>> might share a single pasid table. That will result in an issue.
>>
>> For an example, device A is assigned to access the memory space of
>> process A, and device B is assigned to access the memory space of
>> process B. The dma remapping infrastructure looks like:
>>
>> .------------------.
>> .----------------. | |
>> | | | |
>> .----------------. | Paging structure |
>> | PASID X |--| | for Process A |
>> .----------------. | | |
>> | | --->'------------------'
>> .----------------. .----------------.
>> | | | PASID Y |--|
>> .----------------. .----------------. |
>> | Dev_A context |---| | | | .------------------.
>> '----------------' | .----------------. | | |
>> | | | | | | | |
>> '----------------' | .----------------. | | Paging structure |
>> | Dev_B context | -->| | | | for Process B |
>> '----------------'----->'----------------' | | |
>> | | system-wide v-->'------------------'
>> .----------------. pasid table
>> | |
>> '----------------'
>> Intel iommu
>> context table
>>
>>
>> Since dev_A and dev_B share a pasid table, the side effect is that a flawed
>> dev_A might access the memory space of process B (with pasid y). Vice
>> versa,
>> a flawed dev_B might access memory space of process A (with pasid x).
>>
>> What PATCH 4~9 do is to remove such possibility by assigning a pasid table
>> for each pci device. Hence, the remapping infrastructure looks like:
>>
>>
>> .------------------.
>> | |
>> .----------------. | |
>> | | | Paging structure |
>> .----------------. | for Process A |
>> | PASID X | | |
>> .----------------.----->'------------------'
>> | |
>> .----------------.
>> | |
>> .----------------.
>> | |
>> .----------------.
>> .----------------. | |
>> | | .----------------.
>> .----------------. | |
>> | Dev_A context |------>'----------------'
>> '----------------' pasid table
>> | | for Dev_A
>> '----------------'
>> | Dev_B context |-->
>> '----------------' | .----------------.
>> | | | | | .------------------.
>> .----------------. | .----------------. | |
>> | | | | | | |
>> '----------------' | .----------------. | Paging structure |
>> Intel iommu | | | | for Process B |
>> context table | .----------------. | |
>> | | PASID Y |----->'------------------'
>> | .----------------.
>> | | |
>> | .----------------.
>> | | |
>> | .----------------.
>> v--->| |
>> '----------------'
>> pasid table
>> for Dev_B
>>
>>
>> With this, dev_A has no means to access memory of process B and vice
>> versa.
>>
>> Best regards,
>> Lu Baolu

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