linux-kernel - Re: [PATCH v7 11/11] iommu/vt-d: Add svm/sva invalidate function

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Message-ID: <20191028091049.04f2d83f@jacob-builder>
Date:   Mon, 28 Oct 2019 09:10:49 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        "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>,
        "Alex Williamson" <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v7 11/11] iommu/vt-d: Add svm/sva invalidate function

On Mon, 28 Oct 2019 06:06:33 +0000
"Tian, Kevin" <kevin.tian@...el.com> wrote:

> > >>> +    /* PASID based dev TLBs, only support all PASIDs or single
> > >>> PASID */
> > >>> +    {1, 1, 0},  
> > >>
> > >> I forgot previous discussion. is it necessary to pass down dev
> > >> TLB invalidation
> > >> requests? Can it be handled by host iOMMU driver automatically?  
> > >
> > > On host SVA, when a memory is unmapped, driver callback will
> > > invalidate dev IOTLB explicitly. So I guess we need to pass down
> > > it for guest case. This is also required for guest iova over 1st
> > > level usage as far as can see.
> > >  
> > 
> > Sorry, I confused guest vIOVA and guest vSVA. For guest vIOVA, no
> > device TLB invalidation pass down. But currently for guest vSVA,
> > device TLB invalidation is passed down. Perhaps we can avoid
> > passing down dev TLB flush just like what we are doing for guest
> > IOVA. 
> 
> I think dev TLB is fully handled within IOMMU driver today. It doesn't
> require device driver to explicit toggle. With this then we can fully
> virtualize guest dev TLB invalidation request to save one syscall,
> since the host is supposed to flush dev TLB when serving the earlier
> IOTLB invalidation pass-down.

In the previous discussions, we thought about making IOTLB flush
inclusive, where IOTLB flush would always include device TLB flush. But
we thought such behavior cannot be assumed for all VMMs, some may still
do explicit dev TLB flush. So for completeness, we included dev TLB
here.