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From: David Gibson <david@gibson.dropbear.id.au>
To: Ram Pai <linuxram@us.ibm.com>
Cc: andmike@us.ibm.com, sukadev@linux.vnet.ibm.com,
	mdroth@linux.vnet.ibm.com, b.zolnierkie@samsung.com,
	jasowang@redhat.com, aik@linux.ibm.com,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	iommu@lists.linux-foundation.org, paul.burton@mips.com,
	m.szyprowski@samsung.com, linuxppc-dev@lists.ozlabs.org,
	hch@lst.de, robin.murphy@arm.com
Subject: Re: [PATCH 2/2] virtio_ring: Use DMA API if memory is encrypted
Date: Mon, 14 Oct 2019 15:52:35 +1100
Message-ID: <20191014045235.GO4080@umbus.fritz.box> (raw)
In-Reply-To: <1570843519-8696-3-git-send-email-linuxram@us.ibm.com>

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On Fri, Oct 11, 2019 at 06:25:19PM -0700, Ram Pai wrote:
> From: Thiago Jung Bauermann <bauerman@linux.ibm.com>
> 
> Normally, virtio enables DMA API with VIRTIO_F_IOMMU_PLATFORM, which must
> be set by both device and guest driver. However, as a hack, when DMA API
> returns physical addresses, guest driver can use the DMA API; even though
> device does not set VIRTIO_F_IOMMU_PLATFORM and just uses physical
> addresses.
> 
> Doing this works-around POWER secure guests for which only the bounce
> buffer is accessible to the device, but which don't set
> VIRTIO_F_IOMMU_PLATFORM due to a set of hypervisor and architectural bugs.
> To guard against platform changes, breaking any of these assumptions down
> the road, we check at probe time and fail if that's not the case.
> 
> cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> cc: David Gibson <david@gibson.dropbear.id.au>
> cc: Michael Ellerman <mpe@ellerman.id.au>
> cc: Paul Mackerras <paulus@ozlabs.org>
> cc: Michael Roth <mdroth@linux.vnet.ibm.com>
> cc: Alexey Kardashevskiy <aik@linux.ibm.com>
> cc: Jason Wang <jasowang@redhat.com>
> cc: Christoph Hellwig <hch@lst.de>
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

I don't know that this is the most elegant solution possible.  But
it's simple, gets the job done and pretty unlikely to cause mysterious
breakage down the road.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-12  1:25 [PATCH 0/2] virtio: Support encrypted memory on powerpc secure guests Ram Pai
2019-10-12  1:25 ` [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr() Ram Pai
2019-10-12  1:25   ` [PATCH 2/2] virtio_ring: Use DMA API if memory is encrypted Ram Pai
2019-10-14  4:52     ` David Gibson [this message]
2019-10-15  7:35     ` Christoph Hellwig
2019-10-16  7:55       ` Ram Pai
2019-10-17  2:33       ` Jason Wang
2019-10-21  8:36       ` David Gibson
2019-10-14  4:51   ` [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr() David Gibson
2019-10-14 10:29     ` Robin Murphy
2019-10-15  7:30       ` Ram Pai
2019-10-15  7:31       ` Christoph Hellwig
2019-10-12  1:36 ` [PATCH 0/2] virtio: Support encrypted memory on powerpc secure guests Ram Pai

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