Re: [RFC KERNEL PATCH v7 2/2] xen/privcmd: Add new syscall to get gsi from dev

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 15 May 2024, Jiqian Chen wrote:
> In PVH dom0, it uses the linux local interrupt mechanism,
> when it allocs irq for a gsi, it is dynamic, and follow
> the principle of applying first, distributing first. And
> the irq number is alloced from small to large, but the
> applying gsi number is not, may gsi 38 comes before gsi 28,
> it causes the irq number is not equal with the gsi number.
> And when passthrough a device, QEMU will use device's gsi
> number to do pirq mapping, but the gsi number is got from
> file /sys/bus/pci/devices/<sbdf>/irq, irq!= gsi, so it will
> fail when mapping.
> 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.
> 
> Co-developed-by: Huang Rui <ray.huang@xxxxxxx>
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
>  drivers/xen/privcmd.c              | 28 ++++++++++++++++++++++
>  drivers/xen/xen-pciback/pci_stub.c | 38 +++++++++++++++++++++++++++---
>  include/uapi/xen/privcmd.h         |  7 ++++++
>  include/xen/acpi.h                 |  2 ++
>  4 files changed, 72 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 67dfa4778864..5953a03b5cb0 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -45,6 +45,9 @@
>  #include <xen/page.h>
>  #include <xen/xen-ops.h>
>  #include <xen/balloon.h>
> +#ifdef CONFIG_ACPI
> +#include <xen/acpi.h>
> +#endif
>  
>  #include "privcmd.h"
>  
> @@ -842,6 +845,27 @@ static long privcmd_ioctl_mmap_resource(struct file 
> *file,
>       return rc;
>  }
>  
> +static long privcmd_ioctl_gsi_from_dev(struct file *file, void __user *udata)
> +{
> +     struct privcmd_gsi_from_dev kdata;
> +
> +     if (copy_from_user(&kdata, udata, sizeof(kdata)))
> +             return -EFAULT;
> +
> +#ifdef CONFIG_ACPI
> +     kdata.gsi = pcistub_get_gsi_from_sbdf(kdata.sbdf);
> +     if (kdata.gsi == -1)
> +             return -EINVAL;
> +#else
> +     kdata.gsi = -1;

Should we return an error instead, like -EINVAL, to make the behavior
more similar to the CONFIG_ACPI case?


> +#endif
> +
> +     if (copy_to_user(udata, &kdata, sizeof(kdata)))
> +             return -EFAULT;
> +
> +     return 0;
> +}
> +
>  #ifdef CONFIG_XEN_PRIVCMD_EVENTFD
>  /* Irqfd support */
>  static struct workqueue_struct *irqfd_cleanup_wq;
> @@ -1529,6 +1553,10 @@ static long privcmd_ioctl(struct file *file,
>               ret = privcmd_ioctl_ioeventfd(file, udata);
>               break;
>  
> +     case IOCTL_PRIVCMD_GSI_FROM_DEV:
> +             ret = privcmd_ioctl_gsi_from_dev(file, udata);
> +             break;
> +
>       default:
>               break;
>       }
> diff --git a/drivers/xen/xen-pciback/pci_stub.c 
> b/drivers/xen/xen-pciback/pci_stub.c
> index 2b90d832d0a7..4b62b4d377a9 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_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_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_ACPI
> +int pcistub_get_gsi_from_sbdf(unsigned int sbdf)
> +{
> +     struct pcistub_device *psdev;
> +     int domain = sbdf >> 16;
> +     int bus = (sbdf >> 8) & 0xff;
> +     int slot = (sbdf >> 3) & 0x1f;
> +     int func = sbdf & 0x7;

you can use PCI_DEVFN PCI_SLOT PCI_FUNC pci_domain_nr instead of open
coding.


> +
> +     psdev = pcistub_device_find(domain, bus, slot, func);
> +
> +     if (!psdev)
> +             return -1;
> +
> +     return psdev->gsi;
> +}
> +EXPORT_SYMBOL_GPL(pcistub_get_gsi_from_sbdf);
> +#endif
> +
>  struct pci_dev *pcistub_get_pci_dev_by_slot(struct xen_pcibk_device *pdev,
>                                           int domain, int bus,
>                                           int slot, int func)
> @@ -367,14 +392,20 @@ static int pcistub_match(struct pci_dev *dev)
>       return found;
>  }
>  
> -static int pcistub_init_device(struct pci_dev *dev)
> +static int pcistub_init_device(struct pcistub_device *psdev)
>  {
>       struct xen_pcibk_dev_data *dev_data;
> +     struct pci_dev *dev;
>  #ifdef CONFIG_ACPI
>       int gsi, trigger, polarity;
>  #endif
>       int err = 0;
>  
> +     if (!psdev)
> +             return -EINVAL;
> +
> +     dev = psdev->dev;
> +
>       dev_dbg(&dev->dev, "initializing...\n");
>  
>       /* The PCI backend is not intended to be a module (or to work with
> @@ -448,6 +479,7 @@ static int pcistub_init_device(struct pci_dev *dev)
>               dev_err(&dev->dev, "Fail to get gsi info!\n");
>               goto config_release;
>       }
> +     psdev->gsi = gsi;
>  
>       if (xen_initial_domain() && xen_pvh_domain()) {
>               err = xen_pvh_setup_gsi(gsi, trigger, polarity);
> @@ -495,7 +527,7 @@ static int __init pcistub_init_devices_late(void)
>  
>               spin_unlock_irqrestore(&pcistub_devices_lock, flags);
>  
> -             err = pcistub_init_device(psdev->dev);
> +             err = pcistub_init_device(psdev);
>               if (err) {
>                       dev_err(&psdev->dev->dev,
>                               "error %d initializing device\n", err);
> @@ -565,7 +597,7 @@ static int pcistub_seize(struct pci_dev *dev,
>               spin_unlock_irqrestore(&pcistub_devices_lock, flags);
>  
>               /* don't want irqs disabled when calling pcistub_init_device */
> -             err = pcistub_init_device(psdev->dev);
> +             err = pcistub_init_device(psdev);
>  
>               spin_lock_irqsave(&pcistub_devices_lock, flags);
>  
> diff --git a/include/uapi/xen/privcmd.h b/include/uapi/xen/privcmd.h
> index 8b8c5d1420fe..220e7670a113 100644
> --- a/include/uapi/xen/privcmd.h
> +++ b/include/uapi/xen/privcmd.h
> @@ -126,6 +126,11 @@ struct privcmd_ioeventfd {
>       __u8 pad[2];
>  };
>  
> +struct privcmd_gsi_from_dev {
> +     __u32 sbdf;
> +     int gsi;
> +};
> +
>  /*
>   * @cmd: IOCTL_PRIVCMD_HYPERCALL
>   * @arg: &privcmd_hypercall_t
> @@ -157,5 +162,7 @@ struct privcmd_ioeventfd {
>       _IOW('P', 8, struct privcmd_irqfd)
>  #define IOCTL_PRIVCMD_IOEVENTFD                                      \
>       _IOW('P', 9, struct privcmd_ioeventfd)
> +#define IOCTL_PRIVCMD_GSI_FROM_DEV                           \
> +     _IOC(_IOC_NONE, 'P', 10, sizeof(struct privcmd_gsi_from_dev))
>  
>  #endif /* __LINUX_PUBLIC_PRIVCMD_H__ */
> diff --git a/include/xen/acpi.h b/include/xen/acpi.h
> index 9b50027113f3..0bf5f4884456 100644
> --- a/include/xen/acpi.h
> +++ b/include/xen/acpi.h
> @@ -83,4 +83,6 @@ int xen_acpi_get_gsi_info(struct pci_dev *dev,
>                                                 int *gsi_out,
>                                                 int *trigger_out,
>                                                 int *polarity_out);
> +
> +int pcistub_get_gsi_from_sbdf(unsigned int sbdf);
>  #endif       /* _XEN_ACPI_H */
> -- 
> 2.34.1
>