linux-kernel - [RFC PATCH 06/11] powerpc/svm: Use SWIOTLB DMA API for all virtio devices

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Date:   Thu, 23 Aug 2018 23:59:28 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Anshuman Khandual <anshuman.linux@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christoph Hellwig <hch@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mike Anderson <andmike@...ux.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Ram Pai <linuxram@...ibm.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Subject: [RFC PATCH 06/11] powerpc/svm: Use SWIOTLB DMA API for all virtio devices

From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>

Secure guest memory (GPA range) is isolated and inaccessible from the host.
But virtio ring transactions require the back end drivers to process
incoming scatter gather buffers which require their access in host. Hence a
portion of guest memory can be converted to shared memory and all buffers
need to be bounced into the pool before being passed on to the host.

SWIOTLB buffers can be pre-allocated and converted as shared memory during
early boot. Generic SWIOTLB DMA API (swiotlb_dma_ops) callbacks can be used
to bounce each incoming scatter gather I/O buffer addresses into this pool
of shared memory before being passed on to the host. All virtio devices on
secure guest platform need to use generic SWIOTLB DMA API. Utilize the new
virtio core platform hook platform_override_dma_ops() to achieve this.

Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
---
 arch/powerpc/platforms/pseries/iommu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index 5773bc7eb4bd..56b894d65dba 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -39,6 +39,7 @@
 #include <linux/iommu.h>
 #include <linux/rculist.h>
 #include <linux/virtio.h>
+#include <linux/virtio_config.h>
 #include <asm/io.h>
 #include <asm/prom.h>
 #include <asm/rtas.h>
@@ -51,6 +52,7 @@
 #include <asm/udbg.h>
 #include <asm/mmzone.h>
 #include <asm/plpar_wrappers.h>
+#include <asm/svm.h>
 
 #include "pseries.h"
 
@@ -1400,5 +1402,7 @@ machine_subsys_initcall_sync(pseries, tce_iommu_bus_notifier_init);
 
 void platform_override_dma_ops(struct virtio_device *vdev)
 {
-	/* Override vdev->parent.dma_ops if required */
+	if (is_svm_platform() &&
+			!virtio_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM))
+		set_dma_ops(vdev->dev.parent, &swiotlb_dma_ops);
 }