Re: [PATCH v5 11/14] vpci: add initial support for virtual PCI bus topology

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Nov 25, 2021 at 01:02:48PM +0200, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> 
> Assign SBDF to the PCI devices being passed through with bus 0.
> The resulting topology is where PCIe devices reside on the bus 0 of the
> root complex itself (embedded endpoints).
> This implementation is limited to 32 devices which are allowed on
> a single PCI bus.
> 
> Please note, that at the moment only function 0 of a multifunction
> device can be passed through.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> ---
> Since v4:
> - moved and re-worked guest sbdf initializers
> - s/set_bit/__set_bit
> - s/clear_bit/__clear_bit
> - minor comment fix s/Virtual/Guest/
> - added VPCI_MAX_VIRT_DEV constant (PCI_SLOT(~0) + 1) which will be used
>   later for counting the number of MMIO handlers required for a guest
>   (Julien)
> Since v3:
>  - make use of VPCI_INIT
>  - moved all new code to vpci.c which belongs to it
>  - changed open-coded 31 to PCI_SLOT(~0)
>  - added comments and code to reject multifunction devices with
>    functions other than 0
>  - updated comment about vpci_dev_next and made it unsigned int
>  - implement roll back in case of error while assigning/deassigning devices
>  - s/dom%pd/%pd
> Since v2:
>  - remove casts that are (a) malformed and (b) unnecessary
>  - add new line for better readability
>  - remove CONFIG_HAS_VPCI_GUEST_SUPPORT ifdef's as the relevant vPCI
>     functions are now completely gated with this config
>  - gate common code with CONFIG_HAS_VPCI_GUEST_SUPPORT
> New in v2
> ---
>  xen/drivers/vpci/vpci.c | 51 +++++++++++++++++++++++++++++++++++++++++
>  xen/include/xen/sched.h |  8 +++++++
>  xen/include/xen/vpci.h  | 11 +++++++++
>  3 files changed, 70 insertions(+)
> 
> diff --git a/xen/drivers/vpci/vpci.c b/xen/drivers/vpci/vpci.c
> index 98b12a61be6f..c2fb4d4db233 100644
> --- a/xen/drivers/vpci/vpci.c
> +++ b/xen/drivers/vpci/vpci.c
> @@ -114,6 +114,9 @@ int vpci_add_handlers(struct pci_dev *pdev)
>      spin_lock(&pdev->vpci_lock);
>      pdev->vpci = vpci;
>      INIT_LIST_HEAD(&pdev->vpci->handlers);
> +#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +    pdev->vpci->guest_sbdf.sbdf = ~0;
> +#endif
>  
>      header = &pdev->vpci->header;
>      for ( i = 0; i < ARRAY_SIZE(header->bars); i++ )
> @@ -145,6 +148,53 @@ int vpci_add_handlers(struct pci_dev *pdev)
>  }
>  
>  #ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +int vpci_add_virtual_device(struct pci_dev *pdev)
> +{
> +    struct domain *d = pdev->domain;
> +    pci_sbdf_t sbdf = { 0 };
> +    unsigned long new_dev_number;

I think this needs to be limited to non-hardware domains?

Or else you will report failures for the hardware domain even if it's
not using the virtual topology at all.

> +    /*
> +     * Each PCI bus supports 32 devices/slots at max or up to 256 when
> +     * there are multi-function ones which are not yet supported.
> +     */
> +    if ( pdev->info.is_extfn )
> +    {
> +        gdprintk(XENLOG_ERR, "%pp: only function 0 passthrough supported\n",
> +                 &pdev->sbdf);
> +        return -EOPNOTSUPP;
> +    }
> +
> +    new_dev_number = find_first_zero_bit(&d->vpci_dev_assigned_map,
> +                                         VPCI_MAX_VIRT_DEV);
> +    if ( new_dev_number >= VPCI_MAX_VIRT_DEV )
> +        return -ENOSPC;
> +
> +    __set_bit(new_dev_number, &d->vpci_dev_assigned_map);

How is vpci_dev_assigned_map protected from concurrent accesses? Does
it rely on the pcidevs lock being held while accessing it?

If so it needs spelling out (and likely an assert added).

> +    /*
> +     * Both segment and bus number are 0:
> +     *  - we emulate a single host bridge for the guest, e.g. segment 0
> +     *  - with bus 0 the virtual devices are seen as embedded
> +     *    endpoints behind the root complex
> +     *
> +     * TODO: add support for multi-function devices.
> +     */
> +    sbdf.devfn = PCI_DEVFN(new_dev_number, 0);
> +    pdev->vpci->guest_sbdf = sbdf;
> +
> +    return 0;
> +
> +}
> +REGISTER_VPCI_INIT(vpci_add_virtual_device, VPCI_PRIORITY_MIDDLE);

I'm unsure this is the right place to do virtual SBDF assignment, my
plan was to use REGISTER_VPCI_INIT exclusively with PCI capabilities.

I think it would be better to do the virtual SBDF assignment from
vpci_assign_device.

> +
> +static void vpci_remove_virtual_device(struct domain *d,
> +                                       const struct pci_dev *pdev)
> +{
> +    __clear_bit(pdev->vpci->guest_sbdf.dev, &d->vpci_dev_assigned_map);
> +    pdev->vpci->guest_sbdf.sbdf = ~0;
> +}
> +
>  /* Notify vPCI that device is assigned to guest. */
>  int vpci_assign_device(struct domain *d, struct pci_dev *pdev)
>  {
> @@ -171,6 +221,7 @@ int vpci_deassign_device(struct domain *d, struct pci_dev 
> *pdev)
>          return 0;
>  
>      spin_lock(&pdev->vpci_lock);
> +    vpci_remove_virtual_device(d, pdev);
>      vpci_remove_device_handlers_locked(pdev);
>      spin_unlock(&pdev->vpci_lock);
>  
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 28146ee404e6..10bff103317c 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -444,6 +444,14 @@ struct domain
>  
>  #ifdef CONFIG_HAS_PCI
>      struct list_head pdev_list;
> +#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +    /*
> +     * The bitmap which shows which device numbers are already used by the
> +     * virtual PCI bus topology and is used to assign a unique SBDF to the
> +     * next passed through virtual PCI device.
> +     */
> +    unsigned long vpci_dev_assigned_map;

Please use DECLARE_BITMAP with the maximum number of supported
devices as parameter.

> +#endif
>  #endif
>  
>  #ifdef CONFIG_HAS_PASSTHROUGH
> diff --git a/xen/include/xen/vpci.h b/xen/include/xen/vpci.h
> index 18319fc329f9..e5258bd7ce90 100644
> --- a/xen/include/xen/vpci.h
> +++ b/xen/include/xen/vpci.h
> @@ -21,6 +21,13 @@ typedef int vpci_register_init_t(struct pci_dev *dev);
>  
>  #define VPCI_ECAM_BDF(addr)     (((addr) & 0x0ffff000) >> 12)
>  
> +/*
> + * Maximum number of devices supported by the virtual bus topology:
> + * each PCI bus supports 32 devices/slots at max or up to 256 when
> + * there are multi-function ones which are not yet supported.
> + */
> +#define VPCI_MAX_VIRT_DEV       (PCI_SLOT(~0) + 1)
> +
>  #define REGISTER_VPCI_INIT(x, p)                \
>    static vpci_register_init_t *const x##_entry  \
>                 __used_section(".data.vpci." p) = x
> @@ -143,6 +150,10 @@ struct vpci {
>              struct vpci_arch_msix_entry arch;
>          } entries[];
>      } *msix;
> +#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +    /* Guest SBDF of the device. */
> +    pci_sbdf_t guest_sbdf;
> +#endif
>  #endif
>  };
>  
> -- 
> 2.25.1
>