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SubjectRe: [Xen-devel] [RFC] virtio_ring: check dma_mem for xen_domain
On Mon, 21 Jan 2019, Peng Fan wrote:
> on i.MX8QM, M4_1 is communicating with DomU using rpmsg with a fixed
> address as the dma mem buffer which is predefined.
>
> Without this patch, the flow is:
> vring_map_one_sg -> vring_use_dma_api
> -> dma_map_page
> -> __swiotlb_map_page
> ->swiotlb_map_page
> ->__dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
> However we are using per device dma area for rpmsg, phys_to_virt
> could not return a correct virtual address for virtual address in
> vmalloc area. Then kernel panic.
>
> With this patch, vring_use_dma_api will return false, and
> vring_map_one_sg will return sg_phys(sg) which is the correct phys
> address in the predefined memory region.
> vring_map_one_sg -> vring_use_dma_api
> -> sg_phys(sg)
>
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
> drivers/virtio/virtio_ring.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index cd7e755484e3..8993d7cb3592 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -248,6 +248,8 @@ static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
>
> static bool vring_use_dma_api(struct virtio_device *vdev)
> {
> + struct device *dma_dev = vdev->dev.parent;
> +
> if (!virtio_has_iommu_quirk(vdev))
> return true;
>
> @@ -260,7 +262,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
> * the DMA API if we're a Xen guest, which at least allows
> * all of the sensible Xen configurations to work correctly.
> */
> - if (xen_domain())
> + if (xen_domain() && !dma_dev->dma_mem)
> return true;
>
> return false;

I can see you spotted a real issue, but this is not the right fix. We
just need something a bit more flexible than xen_domain(): there are
many kinds of Xen domains on different architectures, we basically want
to enable this (return true from vring_use_dma_api) only when the xen
swiotlb is meant to be used. Does the appended patch fix the issue you
have?

---

xen: introduce xen_vring_use_dma

From: Stefano Stabellini <stefanos@xilinx.com>

Export xen_swiotlb on arm and arm64.

Use xen_swiotlb to determine when vring should use dma APIs to map the
ring: when xen_swiotlb is enabled the dma API is required. When it is
disabled, it is not required.

Reported-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>

diff --git a/arch/arm/include/asm/xen/swiotlb-xen.h b/arch/arm/include/asm/xen/swiotlb-xen.h
new file mode 100644
index 0000000..455ade5
--- /dev/null
+++ b/arch/arm/include/asm/xen/swiotlb-xen.h
@@ -0,0 +1 @@
+#include <xen/arm/swiotlb-xen.h>
diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index cb44aa2..8592863 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -21,6 +21,8 @@
#include <asm/xen/hypercall.h>
#include <asm/xen/interface.h>

+int xen_swiotlb __read_mostly;
+
unsigned long xen_get_swiotlb_free_pages(unsigned int order)
{
struct memblock_region *reg;
@@ -189,6 +191,7 @@ int __init xen_mm_init(void)
struct gnttab_cache_flush cflush;
if (!xen_initial_domain())
return 0;
+ xen_swiotlb = 1;
xen_swiotlb_init(1, false);
xen_dma_ops = &xen_swiotlb_dma_ops;

diff --git a/arch/arm64/include/asm/xen/swiotlb-xen.h b/arch/arm64/include/asm/xen/swiotlb-xen.h
new file mode 100644
index 0000000..455ade5
--- /dev/null
+++ b/arch/arm64/include/asm/xen/swiotlb-xen.h
@@ -0,0 +1 @@
+#include <xen/arm/swiotlb-xen.h>
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index cd7e755..bf8badc 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -260,7 +260,7 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
* the DMA API if we're a Xen guest, which at least allows
* all of the sensible Xen configurations to work correctly.
*/
- if (xen_domain())
+ if (xen_vring_use_dma())
return true;

return false;
diff --git a/include/xen/arm/swiotlb-xen.h b/include/xen/arm/swiotlb-xen.h
new file mode 100644
index 0000000..2aac7c4
--- /dev/null
+++ b/include/xen/arm/swiotlb-xen.h
@@ -0,0 +1,10 @@
+#ifndef _ASM_ARM_XEN_SWIOTLB_XEN_H
+#define _ASM_ARM_XEN_SWIOTLB_XEN_H
+
+#ifdef CONFIG_SWIOTLB_XEN
+extern int xen_swiotlb;
+#else
+#define xen_swiotlb (0)
+#endif
+
+#endif
diff --git a/include/xen/xen.h b/include/xen/xen.h
index 0e21567..74a536d 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -46,4 +46,10 @@ enum xen_domain_type {
bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
const struct bio_vec *vec2);

+#include <asm/xen/swiotlb-xen.h>
+static inline int xen_vring_use_dma(void)
+{
+ return !!xen_swiotlb;
+}
+
#endif /* _XEN_XEN_H */
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