Re: [Xen-devel] [RFC] virtio_ring: check dma_mem for xen_domain

[Peng Fan <peng.fan@xxxxxxx>]

> -----Original Message-----
> From: Stefano Stabellini [mailto:sstabellini@xxxxxxxxxx]
> Sent: 2019年1月23日 4:00
> To: Peng Fan <peng.fan@xxxxxxx>
> Cc: mst@xxxxxxxxxx; jasowang@xxxxxxxxxx; sstabellini@xxxxxxxxxx;
> hch@xxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> linux-remoteproc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; luto@xxxxxxxxxx; jgross@xxxxxxxx;
> boris.ostrovsky@xxxxxxxxxx
> Subject: Re: [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@xxxxxxx>
> > ---
> >  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@xxxxxxxxxx>
> 
> 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@xxxxxxx>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> 
> 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 */

Tested-by: Peng Fan <peng.fan@xxxxxxx>

Thanks,
Peng
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