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Re: [PATCH V2] xen/virtio: Handle PCI devices which Host controller is described in DT

On 10/19/22 22:41, Oleksandr Tyshchenko wrote:

Hi Oleksandr



On 19.10.22 11:47, Xenia Ragiadakou wrote:

Hello Xenia


On 10/19/22 03:58, Stefano Stabellini wrote:

On Sat, 15 Oct 2022, Oleksandr Tyshchenko wrote:

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

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).

So use generic PCI-IOMMU bindings instead (iommu-map/iommu-map-mask
properties) which allows us to describe relationship between PCI
devices and backend domains ID properly.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>


Now that I understood the approach and the reasons for it, I can review
the patch :-)

Please add an example of the bindings in the commit message.



---
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

Previous discussion is at:
https://urldefense.com/v3/__https://lore.kernel.org/xen-devel/20221006174804.2003029-1-olekstysh@xxxxxxxxx/__;!!GF_29dbcQIUBPA!3-vq7Edm3XfKtD5cnNjnOzDQvuo_XrhJ73yH-nPfqOkGGU0IjLG7R7MR_nAJCAPeOutHRLT44wKYwQwz3SauACie_ZAy$
[lore[.]kernel[.]org]

Based on:
https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git/log/?h=for-linus-6.1__;!!GF_29dbcQIUBPA!3-vq7Edm3XfKtD5cnNjnOzDQvuo_XrhJ73yH-nPfqOkGGU0IjLG7R7MR_nAJCAPeOutHRLT44wKYwQwz3SauAEnMDHAq$
[git[.]kernel[.]org]
---
   drivers/xen/grant-dma-ops.c | 87
++++++++++++++++++++++++++++++++-----
   1 file changed, 76 insertions(+), 11 deletions(-)

diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index daa525df7bdc..b79d9d6ce154 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 +293,55 @@ static const struct dma_map_ops
xen_grant_dma_ops = {
       .dma_supported = xen_grant_dma_supported,
   };
   +static struct device_node *xen_dt_get_pci_host_node(struct device
*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);
+}


It seems silly that we need to walk the hierachy that way, but I
couldn't find another way to do it



+static struct device_node *xen_dt_get_node(struct device *dev)
+{
+    if (dev_is_pci(dev))
+        return xen_dt_get_pci_host_node(dev);
+
+    return of_node_get(dev->of_node);
+}
+
+static int xen_dt_map_id(struct device *dev, struct device_node
**iommu_np,
+             u32 *sid)
+{
+    struct pci_dev *pdev = to_pci_dev(dev);
+    u32 rid = PCI_DEVID(pdev->bus->number, pdev->devfn);
+    struct device_node *host_np;
+    int ret;
+
+    host_np = xen_dt_get_pci_host_node(dev);
+    if (!host_np)
+        return -ENODEV;
+
+    ret = of_map_id(host_np, rid, "iommu-map", "iommu-map-mask",
iommu_np, sid);
+    of_node_put(host_np);
+    return ret;
+}
+
   static bool xen_is_dt_grant_dma_device(struct device *dev)
   {
-    struct device_node *iommu_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)) {
+        if (xen_dt_map_id(dev, &iommu_np, NULL))
+            return false;
+    } else
+        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);
@@ -307,9 +351,17 @@ 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);
+        of_node_put(np);
+        return ret;
+    }


We don't need to walk the PCI hierachy twice. Maybe we can add the
of_node check directly to xen_is_dt_grant_dma_device?



I think in general we could pass directly the host bridge device if
dev_is_pci(dev) (which can be retrieved with
pci_get_host_bridge_device(to_pci_dev(dev), and after done with it
pci_put_host_bridge_device(phb)).
So that, xen_is_dt_grant_dma_device() and
xen_dt_grant_init_backend_domid() won't need to discover it themselves.
This will simplify the code.



Good point. I have some remark. Can we use pci_find_host_bridge()
instead? This way we don't have to add #include "../pci/pci.h", and have
to drop reference afterwards.

With that xen_dt_get_pci_host_node() will became the following:


static struct device_node *xen_dt_get_pci_host_node(struct device *dev)
{
      struct pci_host_bridge *bridge =
pci_find_host_bridge(to_pci_dev(dev)->bus);

      return of_node_get(bridge->dev.parent->of_node);
}



You are right. I prefer your version instead of the above.



With Stefano's suggestion, we won't walk the PCI hierarchy twice when
executing xen_is_grant_dma_device() for PCI device:

xen_is_grant_dma_device() -> xen_is_dt_grant_dma_device() ->
xen_dt_map_id() -> xen_dt_get_pci_host_node()


What do you think?
I was thinking passing the device_node along with the device in the function arguments. More specifically, of doing this (not tested, just an idea): 

bool xen_is_grant_dma_device(struct device *dev)
{
    struct device_node *np;
    bool has_iommu = false;

    /* XXX Handle only DT devices for now */
    np = xen_dt_get_node(dev);
    if (np)
        has_iommu = xen_is_dt_grant_dma_device(dev, np);
    of_node_put(np);
    return has_iommu;
}

static bool xen_is_dt_grant_dma_device(struct device *dev,
                                       struct device_node *np)
{
    struct device_node *iommu_np = NULL;
    bool has_iommu;

    if (dev_is_pci(dev)) {
        struct pci_dev *pdev = to_pci_dev(dev);
        u32 id = PCI_DEVID(pdev->bus->number, pdev->devfn);
        of_map_id(np, id, "iommu-map", "iommu-map-mask", &iommu_np, NULL);
    } 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);

    return has_iommu;
}
I 'm wondering ... is it possible for the host bridge device node to have the iommus property set? meaning that all of its pci devs will have the same backend? 






       return false;
   }
@@ -325,12 +377,19 @@ 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 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)) {
+        if (xen_dt_map_id(dev, &iommu_spec.np, iommu_spec.args)) {
+            dev_err(dev, "Cannot translate ID\n");
+            return -ESRCH;
+        }
+    } else {
+        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 (!of_device_is_compatible(iommu_spec.np, "xen,grant-dma") ||
@@ -354,6 +413,7 @@ 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 +425,13 @@ 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, data);
+        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







--
Xenia

 

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