Re: IOASID set token

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

Hi Jean,

Just realized I should send this to your Linaro account instead of ARM.
So Hi again :)

On Wed, 1 Jul 2020 23:29:16 -0700
Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:

> Hi Jean,
> 
> Have a question for you on whether we can have a fixed token type for
> ioasid_set.
> 
> Currently, ioasid_set has an arbitrary token. For VT-d vSVA usage, we
> choose mm as ioasid_set token to identify PASIDs within a guest. We
> have multiple in-kernel users of PASIDs such as VFIO, KVM, and VDCM.
> When an IOASID set is created, there is not a good way to communicate
> about the token choices. So we have to let VDCM and KVM *assume* mm
> is used as token, then retrieve ioasid_set based on the token.
> 
> This assumption of "mm as token" is not a reliable SW architecture. So
> we are thinking if we can have an explicit ioasid_set token type where
> mm is used. After all, PASID and mm are closely related.
> 
> The code change might be the following:
> 1. add a flag to indicate token type when ioasid_set is allocated,
> e.g. IOASID_SET_TYPE_MM
> IOASID_SET_TYPE_ANY
> 2. other users of the ioasid_set can query if an mm token exists based
> on the flag IOASID_SET_TYPE_MM, then retrieve the ioasid_set.
> 
> Existing ioasid_set user can still use arbitrary token under the flag
> IOASID_SET_TYPE_ANY
> 
> Would this be an issue for ARM usage?
> 
> Thanks,
> 
> Jacob

[Jacob Pan]
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