linux-kernel - Re: [PATCH v4 05/22] iommu: introduce iommu invalidate API function

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Date:   Wed, 9 May 2018 05:55:30 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Jean Delvare <khali@...ux-fr.org>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "Liu, Yi L" <yi.l.liu@...ux.intel.com>,
        "Liu@...rya.localdomain" <Liu@...rya.localdomain>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 05/22] iommu: introduce iommu invalidate API function

On Tue, 8 May 2018 11:35:00 +0100
Jean-Philippe Brucker <jean-philippe.brucker@....com> wrote:

> Hi Jacob,
> 
> Looks mostly good to me, I just have a couple more comments
> 
> On 04/05/18 19:07, Jacob Pan wrote:
> > Now the passdown invalidation granularities look like:
> > (sorted by coarseness), will send out in v5 patchset soon if no
> > issues.
> > 
> > /**
> >  * enum iommu_inv_granularity - Generic invalidation granularity
> >  *
> >  * @IOMMU_INV_GRANU_DOMAIN:		Device context cache
> > associated with a
> >  *					domain ID.
> >  * @IOMMU_INV_GRANU_DEVICE:		Device context cache
> > associated with a
> >  *					device ID
> >  * @IOMMU_INV_GRANU_DOMAIN_ALL_PASID:	TLB entries or PASID
> > caches of all
> >  *					PASIDs associated with a
> > domain ID
> >  * @IOMMU_INV_GRANU_PASID_SEL:		TLB entries or PASID
> > cache associated
> >  *					with a PASID and a domain
> >  * @IOMMU_INV_GRANU_PAGE_PASID:		TLB entries of
> > selected page range
> >  *					within a PASID
> >  *
> >  * When an invalidation request is passed down to IOMMU to flush
> > translation
> >  * caches, it may carry different granularity levels, which can be
> > specific
> >  * to certain types of translation caches. For an example, PASID
> > selective
> >  * granularity is only applicable PASID cache and IOTLB
> > invalidation but for
> >  * device context caches.  
> 
> Should it be "PASID selective granularity is only applicable to PASID
> cache and IOTLB but not device context caches"?
> 
right, thanks!
> >  * This enum is a collection of granularities for all types of
> > translation
> >  * caches. The idea is to make it easy for IOMMU model specific
> > driver to
> >  * convert from generic to model specific value. Not all
> > combinations between
> >  * translation caches and granularity levels are valid. Each IOMMU
> > driver
> >  * can enforce check based on its own conversion table. The
> > conversion is
> >  * based on 2D look-up with inputs as follows:
> >  * - translation cache types
> >  * - granularity
> >  * No global granularity is allowed in that passdown invalidation
> > for an
> >  * assigned device should only impact the device or domain itself.  
> 
> That last sentence is a bit confusing, because "global granularity"
> might also refer to the "global" TLB flag which is allowed. In my
> opinion you can leave this rationale out, I doubt userspace will ever
> demand a mechanism for global invalidation.
> 
yes, i can leave the last sentence out.
> >  *
> >  *             type |   DTLB    |    TLB    |   PASID   |  CONTEXT
> >  *  granule         |           |           |           |
> >  * -----------------+-----------+-----------+-----------+-----------
> >  *  DOMAIN          |           |           |           |     Y
> >  *  DEVICE          |           |           |           |     Y  
> 
> I can't really see a use-case for DOMAIN and DEVICE. It might make
> more sense to keep only DN_ALL_PASID, which would then also
> invalidate the device context cache. But since they will be very rare
> events, factoring them doesn't seem important.
> 
ok. we have no use for now either, was there for completeness. i will
remove for now.
> >  *  DN_ALL_PASID    |   Y       |   Y       |   Y       |
> >  *  PASID_SEL       |   Y       |   Y       |   Y       |
> >  *  PAGE_PASID      |           |   Y       |           |  
> 
> Why not allow PAGE_PASID+DTLB? We need a way to invalidate individual
> DTLB entries
> 
I was thinking PAGE_PASID+TLB includes PAGE_PASID+DTLB, but you are
right, DTLB should be a 'Y' here.
> Thanks,
> Jean

[Jacob Pan]