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Date: Tue, 25 Oct 2022 16:12:59 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Oleksandr Tyshchenko <olekstysh@...il.com>
cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Catalin Marinas <catalin.marinas@....com>,
Russell King <linux@...linux.org.uk>,
Stefano Stabellini <sstabellini@...nel.org>,
Juergen Gross <jgross@...e.com>,
Xenia Ragiadakou <burzalodowa@...il.com>
Subject: Re: [PATCH V4 1/2] xen/virtio: Optimize the setup of "xen-grant-dma"
devices
On Tue, 25 Oct 2022, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>
> 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@...m.com>
Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>
> ---
> 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
>
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