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Re: [KERNEL PATCH v9 3/3] xen/privcmd: Add new syscall to get gsi from dev


  • To: "Chen, Jiqian" <Jiqian.Chen@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Mon, 23 Sep 2024 09:58:13 +0200
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "Huang, Ray" <Ray.Huang@xxxxxxx>
  • Delivery-date: Mon, 23 Sep 2024 07:58:21 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 23.09.24 07:49, Chen, Jiqian wrote:
On 2024/9/21 05:17, Stefano Stabellini wrote:
On Fri, 20 Sep 2024, Chen, Jiqian wrote:
On 2024/9/19 06:49, Stefano Stabellini wrote:
On Thu, 12 Sep 2024, Jiqian Chen wrote:
On PVH dom0, when passthrough a device to domU, QEMU and xl tools
want to use gsi number to do pirq mapping, see QEMU code
xen_pt_realize->xc_physdev_map_pirq, and xl code
pci_add_dm_done->xc_physdev_map_pirq, but in current codes, the gsi
number is got from file /sys/bus/pci/devices/<sbdf>/irq, that is
wrong, because irq is not equal with gsi, they are in different
spaces, so pirq mapping fails.
And in current linux codes, there is no method to get gsi
for userspace.

For above purpose, record gsi of pcistub devices when init
pcistub and add a new syscall into privcmd to let userspace
can get gsi when they have a need.

Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
---
v8->v9 changes:
Changed the syscall name from "IOCTL_PRIVCMD_GSI_FROM_DEV" to 
"IOCTL_PRIVCMD_PCIDEV_GET_GSI". Also changed the other functions name.
Changed the macro wrapping "pcistub_get_gsi_from_sbdf" from "CONFIG_XEN_ACPI" to 
"CONFIG_XEN_PCIDEV_BACKEND" to fix compile errors reported by CI robot.
Changed the parameter gsi of struct privcmd_pcidev_get_gsi from int to u32.

v7->v8 changes:
In function privcmd_ioctl_gsi_from_dev, return -EINVAL when not confige 
CONFIG_XEN_ACPI.
Used PCI_BUS_NUM PCI_SLOT PCI_FUNC instead of open coding.

v6->v7 changes:
Changed implementation to add a new parameter "gsi" to struct pcistub_device 
and set gsi when pcistub initialize device. Then when userspace wants to get gsi and pass 
sbdf, we can return that gsi.

v5->v6 changes:
Changed implementation to add a new syscall to translate irq to gsi, instead 
adding a new gsi sysfs node, because the pci Maintainer didn't allow to add 
that sysfs node.

v3->v5 changes:
No.

v2->v3 changes:
Suggested by Roger: Abandoned previous implementations that added new syscall 
to get gsi from irq and changed to add a new sysfs node for gsi, then userspace 
can get gsi number from sysfs node.
---
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: 
https://lore.kernel.org/oe-kbuild-all/202406090826.whl6Cb7R-lkp@xxxxxxxxx/
---
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes: 
https://lore.kernel.org/oe-kbuild-all/202405171113.T431PC8O-lkp@xxxxxxxxx/
---
  drivers/xen/privcmd.c              | 30 +++++++++++++++++++++++
  drivers/xen/xen-pciback/pci_stub.c | 38 +++++++++++++++++++++++++++---
  include/uapi/xen/privcmd.h         |  7 ++++++
  include/xen/acpi.h                 |  9 +++++++
  4 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 9563650dfbaf..1ed612d21543 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -46,6 +46,9 @@
  #include <xen/page.h>
  #include <xen/xen-ops.h>
  #include <xen/balloon.h>
+#ifdef CONFIG_XEN_ACPI
+#include <xen/acpi.h>
+#endif
#include "privcmd.h" @@ -844,6 +847,29 @@ static long privcmd_ioctl_mmap_resource(struct file *file,
        return rc;
  }
+static long privcmd_ioctl_pcidev_get_gsi(struct file *file, void __user *udata)
+{
+#ifdef CONFIG_XEN_ACPI
+       int rc;
+       struct privcmd_pcidev_get_gsi kdata;
+
+       if (copy_from_user(&kdata, udata, sizeof(kdata)))
+               return -EFAULT;
+
+       rc = pcistub_get_gsi_from_sbdf(kdata.sbdf);
+       if (rc < 0)
+               return rc;
+
+       kdata.gsi = rc;
+       if (copy_to_user(udata, &kdata, sizeof(kdata)))
+               return -EFAULT;
+
+       return 0;
+#else
+       return -EINVAL;
+#endif
+}
+
  #ifdef CONFIG_XEN_PRIVCMD_EVENTFD
  /* Irqfd support */
  static struct workqueue_struct *irqfd_cleanup_wq;
@@ -1543,6 +1569,10 @@ static long privcmd_ioctl(struct file *file,
                ret = privcmd_ioctl_ioeventfd(file, udata);
                break;
+ case IOCTL_PRIVCMD_PCIDEV_GET_GSI:
+               ret = privcmd_ioctl_pcidev_get_gsi(file, udata);
+               break;
+
        default:
                break;
        }
diff --git a/drivers/xen/xen-pciback/pci_stub.c 
b/drivers/xen/xen-pciback/pci_stub.c
index 8ce27333f54b..2ea8e4075adc 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -56,6 +56,9 @@ struct pcistub_device {
struct pci_dev *dev;
        struct xen_pcibk_device *pdev;/* non-NULL if struct pci_dev is in use */
+#ifdef CONFIG_XEN_ACPI
+       int gsi;
+#endif
  };
/* Access to pcistub_devices & seized_devices lists and the initialize_devices
@@ -88,6 +91,9 @@ static struct pcistub_device *pcistub_device_alloc(struct 
pci_dev *dev)
kref_init(&psdev->kref);
        spin_lock_init(&psdev->lock);
+#ifdef CONFIG_XEN_ACPI
+       psdev->gsi = -1;
+#endif
return psdev;
  }
@@ -220,6 +226,25 @@ static struct pci_dev *pcistub_device_get_pci_dev(struct 
xen_pcibk_device *pdev,
        return pci_dev;
  }
+#ifdef CONFIG_XEN_PCIDEV_BACKEND


This breaks configurations without CONFIG_ACPI and with
CONFIG_XEN_PCIDEV_BACKEND.

Also there should be no dependency between PCIDEV_BACKEND and
pcistub_get_gsi_from_sbdf.

I think we should solve the build issues this way:

- privcmd_ioctl_pcidev_get_gsi should have:
#if defined(CONFIG_XEN_ACPI) && defined(CONFIG_XEN_PCI_STUB)

- here we should have #ifdef CONFIG_XEN_ACPI as you had before


As far as I can tell the above should be able to address all valid
combinations.
This can't pass a combination that:
CONFIG_XEN_ACPI=y
CONFIG_XEN_PCI_STUB=y
CONFIG_XEN_PCIDEV_BACKEND=m
Reported by robot 
https://lore.kernel.org/oe-kbuild-all/202406090826.whl6Cb7R-lkp@xxxxxxxxx/

At this combination, privcmd_ioctl_pcidev_get_gsi can call pcistub_get_gsi_from_sbdf 
because CONFIG_XEN_ACPI and CONFIG_XEN_PCI_STUB are both "y".
But when the compiler tries to find the implementation of 
pcistub_get_gsi_from_sbdf, it fails (ld: vmlinux.o: in function 
`privcmd_ioctl_pcidev_get_gsi':
/home/cjq/code/upstream/kernel_test_robot/linux_xen/build_dir/../drivers/xen/privcmd.c:859: 
undefined reference to `pcistub_get_gsi_from_sbdf'), because the value of CONFIG_XEN_PCIDEV_BACKEND 
is "m" (file drivers/xen/xen-pciback/Makefile shows 
"obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o"), so that xen-pciback is built as a 
module.


The attached .config, with the appended changes on top of your patch
work for me. I have CONFIG_XEN_PCIDEV_BACKEND=m.
Using your attached .config, it also works for me.
The difference between your .config and the config reported by Robot 
(https://download.01.org/0day-ci/archive/20240609/202406090826.whl6Cb7R-lkp@xxxxxxxxx/config)
 is that your CONFIG_XEN_PRIVCMD=m, but Robot's CONFIG_XEN_PRIVCMD=y.

It seems that, with my patch changes, privcmd uses the function implemented by xen-pciback, so if the configuration is 
"CONFIG_XEN_PRIVCMD=m & CONFIG_XEN_PCIDEV_BACKEND=m" or "CONFIG_XEN_PRIVCMD=y & 
CONFIG_XEN_PCIDEV_BACKEND=y", the compilation is OK, but if the configuration is "CONFIG_XEN_PRIVCMD=y & 
CONFIG_XEN_PCIDEV_BACKEND=m", issue happens.

You can change CONFIG_XEN_PRIVCMD from "m" to "y" in your .config, then you 
will fail at:
ld: vmlinux.o: in function `privcmd_ioctl':
privcmd.c:(.text+0x665e42): undefined reference to `pcistub_get_gsi_from_sbdf'

You can do:

        if (IS_REACHABLE(CONFIG_XEN_PCIDEV_BACKEND)) {
                rc = pcistub_get_gsi_from_sbdf(kdata.sbdf);
                if (rc < 0)
                        return rc;
        }

See Documentation/kbuild/kconfig-language.rst in the kernel source tree.


Juergen

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