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

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2024/5/16 06:42, Stefano Stabellini wrote:
> 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?
OK, will return -EINVAL if not config acpi.
Like:
static long privcmd_ioctl_gsi_from_dev(struct file *file, void __user *udata)
{
#ifdef CONFIG_ACPI
        struct privcmd_gsi_from_dev kdata;

        if (copy_from_user(&kdata, udata, sizeof(kdata)))
                return -EFAULT;

        kdata.gsi = pcistub_get_gsi_from_sbdf(kdata.sbdf);
        if (kdata.gsi == -1)
                return -EINVAL;

        if (copy_to_user(udata, &kdata, sizeof(kdata)))
                return -EFAULT;

        return 0;
#else
        return -EINVAL;
#endif
}

> 
> 
>> +#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.
Thanks, will change to use these in next version.
But pci_domain_nr requires passing in pci_dev.
Will change like:
        int domain = (sbdf >> 16) & 0xffff;
        int bus = PCI_BUS_NUM(sbdf);
        int slot = PCI_SLOT(sbdf);
        int func = PCI_FUNC(sbdf);

> 
> 
>> +
>> +    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
>>

-- 
Best regards,
Jiqian Chen.