Re: [PATCH v4 04/11] vpci: add hooks for PCI device assign/de-assign

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.11.2021 07:56, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> 
> When a PCI device gets assigned/de-assigned some work on vPCI side needs
> to be done for that device. Introduce a pair of hooks so vPCI can handle
> that.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> ---
> Since v3:
>  - remove toolstack roll-back description from the commit message
>    as error are to be handled with proper cleanup in Xen itself
>  - remove __must_check
>  - remove redundant rc check while assigning devices
>  - fix redundant CONFIG_HAS_VPCI check for CONFIG_HAS_VPCI_GUEST_SUPPORT
>  - use REGISTER_VPCI_INIT machinery to run required steps on device
>    init/assign: add run_vpci_init helper
> Since v2:
> - define CONFIG_HAS_VPCI_GUEST_SUPPORT so dead code is not compiled
>   for x86
> Since v1:
>  - constify struct pci_dev where possible
>  - do not open code is_system_domain()
>  - extended the commit message
> ---
>  xen/drivers/Kconfig           |  4 +++
>  xen/drivers/passthrough/pci.c |  6 ++++
>  xen/drivers/vpci/vpci.c       | 57 ++++++++++++++++++++++++++++++-----
>  xen/include/xen/vpci.h        | 16 ++++++++++
>  4 files changed, 75 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/drivers/Kconfig b/xen/drivers/Kconfig
> index db94393f47a6..780490cf8e39 100644
> --- 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
> +
>  endmenu
> diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
> index a9d31293ac09..529a4f50aa80 100644
> --- a/xen/drivers/passthrough/pci.c
> +++ b/xen/drivers/passthrough/pci.c
> @@ -873,6 +873,10 @@ static int deassign_device(struct domain *d, uint16_t 
> seg, uint8_t bus,
>      if ( ret )
>          goto out;
>  
> +    ret = vpci_deassign_device(d, pdev);
> +    if ( ret )
> +        goto out;
> +
>      if ( pdev->domain == hardware_domain  )
>          pdev->quarantine = false;
>  
> @@ -1445,6 +1449,8 @@ static int assign_device(struct domain *d, u16 seg, u8 
> bus, u8 devfn, u32 flag)
>          rc = hd->platform_ops->assign_device(d, devfn, pci_to_dev(pdev), 
> flag);
>      }
>  
> +    rc = vpci_assign_device(d, pdev);
> +
>   done:
>      if ( rc )
>          printk(XENLOG_G_WARNING "%pd: assign (%pp) failed (%d)\n",

Don't you need to call vpci_deassign_device() higher up in this
function for the prior owner of the device?

> +#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
> +/* Notify vPCI that device is assigned to guest. */
> +int vpci_assign_device(struct domain *d, struct pci_dev *pdev)
> +{
> +    int rc;
> +
> +    /* It only makes sense to assign for hwdom or guest domain. */
> +    if ( is_system_domain(d) || !has_vpci(d) )
> +        return 0;
> +
> +    vpci_remove_device_handlers(pdev);

This removes handlers in d, not in the prior owner domain. Is this
really intended? And if it really is meant to remove the new domain's
handlers (of which there ought to be none) - why is this necessary?

Jan