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Message-ID: <da0d72d1-3398-8005-1c40-b5f341ff9fc8@gmail.com>
Date: Thu, 20 Oct 2022 11:24:06 +0300
From: Xenia Ragiadakou <burzalodowa@...il.com>
To: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
Cc: "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <olekstysh@...il.com>
Subject: 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@...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://urldefense.com/v3/__https://lore.kernel.org/xen-devel/20221006174804.2003029-1-olekstysh@gmail.com/__;!!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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