linux-kernel - RE: [PATCH v4 2/2] powerpc/pseries/iommu: Use dma_iommu

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Message-Id: <20191203040731.GC12354@oc0525413822.ibm.com>
Date:   Mon, 2 Dec 2019 20:07:31 -0800
From:   Ram Pai <linuxram@...ibm.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>
Cc:     linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        benh@...nel.crashing.org, david@...son.dropbear.id.au,
        paulus@...abs.org, mdroth@...ux.vnet.ibm.com, hch@....de,
        andmike@...ibm.com, sukadev@...ux.vnet.ibm.com, mst@...hat.com,
        ram.n.pai@...il.com, cai@....pw, tglx@...utronix.de,
        bauerman@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: RE: [PATCH v4 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs
 aswell.

On Tue, Dec 03, 2019 at 11:58:18AM +1100, Alexey Kardashevskiy wrote:
> 
> 
> On 02/12/2019 17:45, Ram Pai wrote:
> > Commit edea902c1c1e ("powerpc/pseries/iommu: Don't use dma_iommu_ops on
> > 	       secure guests")
> > disabled dma_iommu_ops path, for secure VMs. The rationale for disabling
> > the dma_iommu_ops path, was to use the dma_direct path, since it had
> > inbuilt support for bounce-buffering through SWIOTLB.
> > 
> > However dma_iommu_ops is functionally much richer. Depending on the
> > capabilities of the platform, it can handle direct DMA; with or without
> > bounce buffering, and it can handle indirect DMA. Hence its better to
> > leverage the richer functionality supported by dma_iommu_ops.
> 
> What exactly do we leverage after applying this patch? afaict things are
> going to work in exact same old way with this applied, no? Thanks,

Yes. You got it right. Another way of saying this is, it reverts the changes.

RP