linux-kernel - Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected

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Date:   Fri, 21 Feb 2020 14:31:21 +0100
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     David Gibson <david@...son.dropbear.id.au>,
        Christoph Hellwig <hch@....de>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Viktor Mihajlovski <mihajlov@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Ram Pai <linuxram@...ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        Michael Mueller <mimu@...ux.ibm.com>
Subject: Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is
 protected

On Fri, 21 Feb 2020 11:41:57 +0800
Jason Wang <jasowang@...hat.com> wrote:

> > I *think* what you are suggesting here is that virtio devices that
> > have !F_IOMMU_PLATFORM should have their dma_ops set up so that the
> > DMA API treats IOVA==PA, which will satisfy what the device expects.  
> 
> 
> Can this work for swiotlb?

It works on s390. I guess it would be the responsibility of however
provides the dma ops for the virtio device to ensure that if 
!F_IOMMU_PLATFORM the addresses are GPA like *mandated* by the VIRTIO
specification.

Regards,
Halil