linux-kernel - [PATCH] virtio: Force DMA restricted devices through DMA API

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Message-Id: <20220719100256.419780-1-keirf@google.com>
Date:   Tue, 19 Jul 2022 10:02:56 +0000
From:   Keir Fraser <keirf@...gle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
Cc:     kernel-team@...roid.com, Keir Fraser <keirf@...gle.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] virtio: Force DMA restricted devices through DMA API

If virtio devices are tagged for "restricted-dma-pool", then that
pool should be used for virtio ring setup, via the DMA API.

In particular, this fixes virtio_balloon for ARM PKVM, where the usual
workaround of setting VIRTIO_F_ACCESS_PLATFORM in the virtio device
doesn't work because the virtio_balloon driver clears the flag. This
seems a more robust fix than fiddling the flag again.

Signed-off-by: Keir Fraser <keirf@...gle.com>
---
 drivers/virtio/virtio_ring.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a5ec724c01d8..12be2607c648 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -12,6 +12,7 @@
 #include <linux/hrtimer.h>
 #include <linux/dma-mapping.h>
 #include <linux/spinlock.h>
+#include <linux/swiotlb.h>
 #include <xen/xen.h>
 
 #ifdef DEBUG
@@ -248,6 +249,13 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
 	if (!virtio_has_dma_quirk(vdev))
 		return true;
 
+	/* If the device is configured to use a DMA restricted pool,
+	 * we had better use it.
+	 */
+	if (IS_ENABLED(CONFIG_DMA_RESTRICTED_POOL) &&
+	    is_swiotlb_for_alloc(vdev->dev.parent))
+		return true;
+
 	/* Otherwise, we are left to guess. */
 	/*
 	 * In theory, it's possible to have a buggy QEMU-supposed
-- 
2.37.0.170.g444d1eabd0-goog