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Message-ID: <19823a2a-bc84-5458-bb69-7ac0c1b81573@gmail.com>
Date: Wed, 19 Oct 2022 11:47:51 +0300
From: Xenia Ragiadakou <burzalodowa@...il.com>
To: Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <olekstysh@...il.com>
Cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH V2] xen/virtio: Handle PCI devices which Host controller
is described in DT
On 10/19/22 03:58, Stefano Stabellini wrote:
> On Sat, 15 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).
>>
>> 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@...m.com>
>
> 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://lore.kernel.org/xen-devel/20221006174804.2003029-1-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 | 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.
>
>> 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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