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Date: Sat, 22 Oct 2022 06:44:06 +0000
From: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
To: Stefano Stabellini <sstabellini@...nel.org>
CC: "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
Oleksandr Tyshchenko <olekstysh@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.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 21.10.22 23:08, Stefano Stabellini wrote:
Hello Stefano
> 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://urldefense.com/v3/__https://lore.kernel.org/xen-devel/20221006174804.2003029-1-olekstysh@gmail.com/__;!!GF_29dbcQIUBPA!3cZiRy0Scq8-dibrxyFGUlAIhwa7UwRmrCAG-qdvkAG5NInYPZ_mbLTMtsZ_F4Gonowkettr-dcRO3TAs_gn-1xcLk77xg$ [lore[.]kernel[.]org]
>> https://urldefense.com/v3/__https://lore.kernel.org/xen-devel/20221015153409.918775-1-olekstysh@gmail.com/__;!!GF_29dbcQIUBPA!3cZiRy0Scq8-dibrxyFGUlAIhwa7UwRmrCAG-qdvkAG5NInYPZ_mbLTMtsZ_F4Gonowkettr-dcRO3TAs_gn-1xwRjX9GQ$ [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!3cZiRy0Scq8-dibrxyFGUlAIhwa7UwRmrCAG-qdvkAG5NInYPZ_mbLTMtsZ_F4Gonowkettr-dcRO3TAs_gn-1zVOy8WKg$ [git[.]kernel[.]org]
>> ---
>> 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.
ok, I will think about such optimization and will provide my thoughts
about it or a patch. But, I think it should be a separate patch (if
needs be),
as in current patch we don't change anything in that regard, we just
implement
"if (dev_is_pci(dev)) { ... }" condition for
xen_is_dt_grant_dma_device() and xen_dt_grant_init_backend_domid().
>
>
>> @@ -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
>>
--
Regards,
Oleksandr Tyshchenko
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