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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 25 Oct 2022, 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: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> 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;
> -- 
> 2.25.1
>