Re: [PATCH v12 11/15] vpci: add initial support for virtual PCI bus topology

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.01.2024 22:51, Stewart Hildebrand wrote:
> --- a/xen/drivers/Kconfig
> +++ b/xen/drivers/Kconfig
> @@ -15,4 +15,8 @@ source "drivers/video/Kconfig"
>  config HAS_VPCI
>       bool
>  
> +config HAS_VPCI_GUEST_SUPPORT
> +     bool
> +     depends on HAS_VPCI

Wouldn't this better be "select", or even just "imply"?

> --- a/xen/drivers/vpci/vpci.c
> +++ b/xen/drivers/vpci/vpci.c
> @@ -40,6 +40,49 @@ extern vpci_register_init_t *const __start_vpci_array[];
>  extern vpci_register_init_t *const __end_vpci_array[];
>  #define NUM_VPCI_INIT (__end_vpci_array - __start_vpci_array)
>  
> +#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +static int add_virtual_device(struct pci_dev *pdev)
> +{
> +    struct domain *d = pdev->domain;
> +    unsigned int new_dev_number;
> +
> +    if ( is_hardware_domain(d) )
> +        return 0;
> +
> +    ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
> +
> +    /*
> +     * 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 && !pdev->info.is_virtfn )
> +    {
> +        gdprintk(XENLOG_ERR, "%pp: only function 0 passthrough supported\n",
> +                 &pdev->sbdf);

The message suggests you ought to check pdev->devfn to have the low
three bits clear. Yet what you check are two booleans.

Further doesn't this require the multi-function bit to be emulated
clear? And finally don't you then also need to disallow assignment of
devices with phantom functions?

> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -484,6 +484,14 @@ struct domain
>       * 2. pdev->vpci->lock
>       */
>      rwlock_t pci_lock;
> +#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.
> +     */
> +    DECLARE_BITMAP(vpci_dev_assigned_map, VPCI_MAX_VIRT_DEV);
> +#endif
>  #endif

With this the 2nd #endif would likely better gain a comment.

> --- 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)

The limit being this means only bus 0 / seg 0 is supported, which I
think the comment would better also say. (In add_virtual_device(),
which has a similar comment, there's then at least a 2nd one saying
so.)

Jan