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Date: Fri, 21 Oct 2022 13:08:36 -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,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Juergen Gross <jgross@...e.com>,
Xenia Ragiadakou <burzalodowa@...il.com>
Subject: Re: [PATCH V3] xen/virtio: Handle PCI devices which Host controller
is described in DT
On Fri, 21 Oct 2022, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
>
> Use the same "xen-grant-dma" device concept for the PCI devices
> behind device-tree based PCI Host controller, but with one modification.
> Unlike for platform devices, we cannot use generic IOMMU bindings
> (iommus property), as we need to support more flexible configuration.
> The problem is that PCI devices under the single PCI Host controller
> may have the backends running in different Xen domains and thus have
> different endpoints ID (backend domains ID).
>
> Add ability to deal with generic PCI-IOMMU bindings (iommu-map/
> iommu-map-mask properties) which allows us to describe relationship
> between PCI devices and backend domains ID properly.
>
> To avoid having to look up for the PCI Host bridge twice and reduce
> the amount of checks pass an extra struct device_node *np to both
> xen_dt_grant_init_backend_domid() and xen_is_dt_grant_dma_device().
> While at it also pass domid_t *backend_domid instead of
> struct xen_grant_dma_data *data to the former.
>
> So with current patch the code expects iommus property for the platform
> devices and iommu-map/iommu-map-mask properties for PCI devices.
>
> The example of generated by the toolstack iommu-map property
> for two PCI devices 0000:00:01.0 and 0000:00:02.0 whose
> backends are running in different Xen domains with IDs 1 and 2
> respectively:
> iommu-map = <0x08 0xfde9 0x01 0x08 0x10 0xfde9 0x02 0x08>;
>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> ---
> Slightly RFC. This is needed to support Xen grant mappings for virtio-pci devices
> on Arm at some point in the future. The Xen toolstack side is not completely ready yet.
> Here, for PCI devices we use more flexible way to pass backend domid to the guest
> than for platform devices.
>
> Changes V1 -> V2:
> - update commit description
> - rebase
> - rework to use generic PCI-IOMMU bindings instead of generic IOMMU bindings
>
> Changes V2 -> V3:
> - update commit description, add an example
> - drop xen_dt_map_id() and squash xen_dt_get_pci_host_node() with
> xen_dt_get_node()
> - pass struct device_node *np to xen_is_dt_grant_dma_device() and
> xen_dt_grant_init_backend_domid()
> - pass domid_t *backend_domid instead of struct xen_grant_dma_data *data
> to xen_dt_grant_init_backend_domid()
>
> Previous discussion is at:
> https://lore.kernel.org/xen-devel/20221006174804.2003029-1-olekstysh@gmail.com/
> https://lore.kernel.org/xen-devel/20221015153409.918775-1-olekstysh@gmail.com/
>
> Based on:
> https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git/log/?h=for-linus-6.1
> ---
> drivers/xen/grant-dma-ops.c | 80 ++++++++++++++++++++++++++++++-------
> 1 file changed, 66 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index daa525df7bdc..76b29d20aeee 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -10,6 +10,7 @@
> #include <linux/module.h>
> #include <linux/dma-map-ops.h>
> #include <linux/of.h>
> +#include <linux/pci.h>
> #include <linux/pfn.h>
> #include <linux/xarray.h>
> #include <linux/virtio_anchor.h>
> @@ -292,12 +293,37 @@ 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)
> +static struct device_node *xen_dt_get_node(struct device *dev)
> {
> - struct device_node *iommu_np;
> + if (dev_is_pci(dev)) {
> + struct pci_dev *pdev = to_pci_dev(dev);
> + struct pci_bus *bus = pdev->bus;
> +
> + /* Walk up to the root bus to look for PCI Host controller */
> + while (!pci_is_root_bus(bus))
> + bus = bus->parent;
> +
> + return of_node_get(bus->bridge->parent->of_node);
> + }
> +
> + return of_node_get(dev->of_node);
> +}
> +
> +static bool xen_is_dt_grant_dma_device(struct device *dev,
> + struct device_node *np)
> +{
> + struct device_node *iommu_np = NULL;
> bool has_iommu;
>
> - iommu_np = of_parse_phandle(dev->of_node, "iommus", 0);
> + if (dev_is_pci(dev)) {
> + struct pci_dev *pdev = to_pci_dev(dev);
> + u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
> +
> + if (of_map_id(np, rid, "iommu-map", "iommu-map-mask", &iommu_np, NULL))
> + return false;
> + } else
> + iommu_np = of_parse_phandle(np, "iommus", 0);
> +
> has_iommu = iommu_np &&
> of_device_is_compatible(iommu_np, "xen,grant-dma");
> of_node_put(iommu_np);
I think we can remove xen_is_dt_grant_dma_device and just call
xen_dt_grant_init_backend_domid passing a NULL backend_domid?
It is a bit annoying that we are basically doing the same device tree
parsing twice in a row given that the callers do:
if (xen_is_grant_dma_device(dev))
xen_grant_setup_dma_ops(dev);
Maybe we could move the backend_domid allocation and setting to
xen_dt_grant_init_backend_domid, which would end up being done from
the xen_is_grant_dma_device() call chain, and only leave setting
dev->dma_ops from xen_grant_setup_dma_ops().
This way the parsing would be done only once? What do you think? This
suggestion is optional, I am OK also with only removing
xen_is_dt_grant_dma_device.
> @@ -307,9 +333,17 @@ static bool xen_is_dt_grant_dma_device(struct device *dev)
>
> bool xen_is_grant_dma_device(struct device *dev)
> {
> + struct device_node *np;
> +
> /* XXX Handle only DT devices for now */
> - if (dev->of_node)
> - return xen_is_dt_grant_dma_device(dev);
> + np = xen_dt_get_node(dev);
> + if (np) {
> + bool ret;
> +
> + ret = xen_is_dt_grant_dma_device(dev, np);
> + of_node_put(np);
> + return ret;
> + }
>
> return false;
> }
> @@ -323,14 +357,26 @@ bool xen_virtio_mem_acc(struct virtio_device *dev)
> }
>
> static int xen_dt_grant_init_backend_domid(struct device *dev,
> - struct xen_grant_dma_data *data)
> + struct device_node *np,
> + domid_t *backend_domid)
> {
> - struct of_phandle_args iommu_spec;
> + struct of_phandle_args iommu_spec = { .args_count = 1 };
>
> - if (of_parse_phandle_with_args(dev->of_node, "iommus", "#iommu-cells",
> - 0, &iommu_spec)) {
> - dev_err(dev, "Cannot parse iommus property\n");
> - return -ESRCH;
> + if (dev_is_pci(dev)) {
> + struct pci_dev *pdev = to_pci_dev(dev);
> + u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
> +
> + if (of_map_id(np, rid, "iommu-map", "iommu-map-mask", &iommu_spec.np,
> + iommu_spec.args)) {
> + dev_err(dev, "Cannot translate ID\n");
> + return -ESRCH;
> + }
> + } else {
> + if (of_parse_phandle_with_args(np, "iommus", "#iommu-cells",
> + 0, &iommu_spec)) {
> + dev_err(dev, "Cannot parse iommus property\n");
> + return -ESRCH;
> + }
> }
>
> if (!of_device_is_compatible(iommu_spec.np, "xen,grant-dma") ||
> @@ -346,7 +392,7 @@ 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;
> }
> @@ -354,6 +400,7 @@ static int xen_dt_grant_init_backend_domid(struct device *dev,
> void xen_grant_setup_dma_ops(struct device *dev)
> {
> struct xen_grant_dma_data *data;
> + struct device_node *np;
>
> data = find_xen_grant_dma_data(dev);
> if (data) {
> @@ -365,8 +412,13 @@ 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))
> + np = xen_dt_get_node(dev);
> + if (np) {
> + int ret;
> +
> + ret = xen_dt_grant_init_backend_domid(dev, np, &data->backend_domid);
> + of_node_put(np);
> + if (ret)
> goto err;
> } else if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT)) {
> dev_info(dev, "Using dom0 as backend\n");
> --
> 2.25.1
>
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