Re: [PATCH V4 1/2] xen/virtio: Optimize the setup of "xen-grant-dma" devices

[Xenia Ragiadakou <burzalodowa@xxxxxxxxx>]

On 10/25/22 19:20, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>
> This is needed to avoid having to parse the same device-tree
> several times for a given device.
>
> For this to work we need to install the xen_virtio_restricted_mem_acc
> callback in Arm's xen_guest_init() which is same callback as x86's
> PV and HVM modes already use and remove the manual assignment in
> xen_setup_dma_ops(). Also we need to split the code to initialize
> backend_domid into a separate function.
>
> Prior to current patch we parsed the device-tree three times:
> 1. xen_setup_dma_ops()->...->xen_is_dt_grant_dma_device()
> 2. xen_setup_dma_ops()->...->xen_dt_grant_init_backend_domid()
> 3. xen_virtio_mem_acc()->...->xen_is_dt_grant_dma_device()
>
> With current patch we parse the device-tree only once in
> xen_virtio_restricted_mem_acc()->...->xen_dt_grant_init_backend_domid()
>
> Other benefits are:
> - Not diverge from x86 when setting up Xen grant DMA ops
> - Drop several global functions
>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Reviewed-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>

I have a question unrelated to the patch.
CONFIG_XEN_VIRTIO_FORCE_GRANT cannot be used to force backend dom0 in 
case xen_dt_grant_init_backend_domid() fails?
> ---
> New patch
> ---
>   arch/arm/xen/enlighten.c    |  2 +-
>   drivers/xen/grant-dma-ops.c | 77 ++++++++++++++-----------------------
>   include/xen/arm/xen-ops.h   |  4 +-
>   include/xen/xen-ops.h       | 16 --------
>   4 files changed, 30 insertions(+), 69 deletions(-)
>
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 93c8ccbf2982..7d59765aef22 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -445,7 +445,7 @@ static int __init xen_guest_init(void)
>                 return 0;
>   
>   	if (IS_ENABLED(CONFIG_XEN_VIRTIO))
> -               virtio_set_mem_acc_cb(xen_virtio_mem_acc);
> +               virtio_set_mem_acc_cb(xen_virtio_restricted_mem_acc);
>   
>   	if (!acpi_disabled)
>                 xen_acpi_guest_init();
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index daa525df7bdc..1e797a043980 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -292,50 +292,20 @@ static const struct dma_map_ops xen_grant_dma_ops = {
>         .dma_supported = xen_grant_dma_supported,
>   };
>   
> -static bool xen_is_dt_grant_dma_device(struct device *dev)
> -{
> -       struct device_node *iommu_np;
> -       bool has_iommu;
> -
> -       iommu_np = of_parse_phandle(dev->of_node, "iommus", 0);
> -       has_iommu = iommu_np &&
> -                   of_device_is_compatible(iommu_np, "xen,grant-dma");
> -       of_node_put(iommu_np);
> -
> -       return has_iommu;
> -}
> -
> -bool xen_is_grant_dma_device(struct device *dev)
> -{
> -       /* XXX Handle only DT devices for now */
> -       if (dev->of_node)
> -               return xen_is_dt_grant_dma_device(dev);
> -
> -       return false;
> -}
> -
> -bool xen_virtio_mem_acc(struct virtio_device *dev)
> -{
> -       if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || xen_pv_domain())
> -               return true;
> -
> -       return xen_is_grant_dma_device(dev->dev.parent);
> -}
> -
>   static int xen_dt_grant_init_backend_domid(struct device *dev,
> -                                          struct xen_grant_dma_data *data)
> +                                          domid_t *backend_domid)
>   {
>         struct of_phandle_args iommu_spec;
>   
>   	if (of_parse_phandle_with_args(dev->of_node, "iommus", "#iommu-cells",
>                         0, &iommu_spec)) {
> -               dev_err(dev, "Cannot parse iommus property\n");
> +               dev_dbg(dev, "Cannot parse iommus property\n");
>                 return -ESRCH;
>         }
>   
>   	if (!of_device_is_compatible(iommu_spec.np, "xen,grant-dma") ||
>                         iommu_spec.args_count != 1) {
> -               dev_err(dev, "Incompatible IOMMU node\n");
> +               dev_dbg(dev, "Incompatible IOMMU node\n");
>                 of_node_put(iommu_spec.np);
>                 return -ESRCH;
>         }
> @@ -346,12 +316,28 @@ static int xen_dt_grant_init_backend_domid(struct device 
> *dev,
>          * The endpoint ID here means the ID of the domain where the
>          * corresponding backend is running
>          */
> -       data->backend_domid = iommu_spec.args[0];
> +       *backend_domid = iommu_spec.args[0];
>   
>   	return 0;
>   }
>   
> -void xen_grant_setup_dma_ops(struct device *dev)
> +static int xen_grant_init_backend_domid(struct device *dev,
> +                                       domid_t *backend_domid)
> +{
> +       int ret = -ENODEV;
> +
> +       if (dev->of_node) {
> +               ret = xen_dt_grant_init_backend_domid(dev, backend_domid);
> +       } else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT) || 
> xen_pv_domain()) {
> +               dev_info(dev, "Using dom0 as backend\n");
> +               *backend_domid = 0;
> +               ret = 0;
> +       }
> +
> +       return ret;
> +}
> +
> +static void xen_grant_setup_dma_ops(struct device *dev, domid_t backend_domid)
>   {
>         struct xen_grant_dma_data *data;
>   
> @@ -365,16 +351,7 @@ void xen_grant_setup_dma_ops(struct device *dev)
>         if (!data)
>                 goto err;
>   
> -	if (dev->of_node) {
> -               if (xen_dt_grant_init_backend_domid(dev, data))
> -                       goto err;
> -       } else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT)) {
> -               dev_info(dev, "Using dom0 as backend\n");
> -               data->backend_domid = 0;
> -       } else {
> -               /* XXX ACPI device unsupported for now */
> -               goto err;
> -       }
> +       data->backend_domid = backend_domid;
>   
>   	if (store_xen_grant_dma_data(dev, data)) {
>                 dev_err(dev, "Cannot store Xen grant DMA data\n");
> @@ -392,12 +369,14 @@ void xen_grant_setup_dma_ops(struct device *dev)
>   
>   bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
>   {
> -       bool ret = xen_virtio_mem_acc(dev);
> +       domid_t backend_domid;
>   
> -	if (ret)
> -               xen_grant_setup_dma_ops(dev->dev.parent);
> +       if (!xen_grant_init_backend_domid(dev->dev.parent, &backend_domid)) {
> +               xen_grant_setup_dma_ops(dev->dev.parent, backend_domid);
> +               return true;
> +       }
>   
> -	return ret;
> +       return false;
>   }
>   
>   MODULE_DESCRIPTION("Xen grant DMA-mapping layer");
> diff --git a/include/xen/arm/xen-ops.h b/include/xen/arm/xen-ops.h
> index b0766a660338..70073f5a2b54 100644
> --- a/include/xen/arm/xen-ops.h
> +++ b/include/xen/arm/xen-ops.h
> @@ -8,9 +8,7 @@
>   static inline void xen_setup_dma_ops(struct device *dev)
>   {
>   #ifdef CONFIG_XEN
> -       if (xen_is_grant_dma_device(dev))
> -               xen_grant_setup_dma_ops(dev);
> -       else if (xen_swiotlb_detect())
> +       if (xen_swiotlb_detect())
>                 dev->dma_ops = &xen_swiotlb_dma_ops;
>   #endif
>   }
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index a34f4271a2e9..47f11bec5e90 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -216,26 +216,10 @@ static inline void xen_preemptible_hcall_end(void) { }
>   #endif /* CONFIG_XEN_PV && !CONFIG_PREEMPTION */
>   
>   #ifdef CONFIG_XEN_GRANT_DMA_OPS
> -void xen_grant_setup_dma_ops(struct device *dev);
> -bool xen_is_grant_dma_device(struct device *dev);
> -bool xen_virtio_mem_acc(struct virtio_device *dev);
>   bool xen_virtio_restricted_mem_acc(struct virtio_device *dev);
>   #else
> -static inline void xen_grant_setup_dma_ops(struct device *dev)
> -{
> -}
> -static inline bool xen_is_grant_dma_device(struct device *dev)
> -{
> -       return false;
> -}
> -
>   struct virtio_device;
>   
> -static inline bool xen_virtio_mem_acc(struct virtio_device *dev)
> -{
> -       return false;
> -}
> -
>   static inline bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
>   {
>         return false;
--
Xenia