Re: [PATCH v3 6/6] vPCI: re-init extended-capability lists when MMCFG availability changed

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

On Thu, Jan 29, 2026 at 02:10:34PM +0100, Jan Beulich wrote:
> When Dom0 informs up about MMCFG usability, this may change whether
> extended capabilities are available (accessible) for devices. Zap what
> might be on record, and re-initialize the list.
> 
> No synchronization is added for the case where devices may already be in
> use. That'll need sorting when (a) DomU support was added and (b) DomU-s
> may run already while Dom0 / hwdom still boots (dom0less, Hyperlaunch).
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> vpci_reinit_ext_capability_list()'s return value isn't checked, as it
> doesn't feel quite right to fail the hypercall because of this. At the
> same time it also doesn't feel quite right to have the function return
> "void". Thoughts?
> ---
> v3: New.
> 
> --- a/xen/arch/x86/physdev.c
> +++ b/xen/arch/x86/physdev.c
> @@ -8,6 +8,8 @@
>  #include <xen/guest_access.h>
>  #include <xen/iocap.h>
>  #include <xen/serial.h>
> +#include <xen/vpci.h>
> +
>  #include <asm/current.h>
>  #include <asm/io_apic.h>
>  #include <asm/msi.h>
> @@ -169,7 +171,10 @@ int cf_check physdev_check_pci_extcfg(st
>  
>      ASSERT(pdev->seg == info->segment);
>      if ( pdev->bus >= info->start_bus && pdev->bus <= info->end_bus )
> +    {
>          pci_check_extcfg(pdev);
> +        vpci_reinit_ext_capability_list(pdev);
> +    }
>  
>      return 0;
>  }
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -869,6 +869,18 @@ static int vpci_init_ext_capability_list
>      return 0;
>  }
>  
> +int vpci_reinit_ext_capability_list(const struct pci_dev *pdev)
> +{
> +    if ( !pdev->vpci )
> +        return 0;
> +
> +    if ( vpci_remove_registers(pdev->vpci, PCI_CFG_SPACE_SIZE,
> +                               PCI_CFG_SPACE_EXP_SIZE - PCI_CFG_SPACE_SIZE) )
> +        ASSERT_UNREACHABLE();
> +
> +    return vpci_init_ext_capability_list(pdev);

Isn't this missing the possible addition or removal of managed
extended capabilities?  IOW: on removal of access to the extended
space the vPCI managed capabilties that have is_ext == true should
call their ->cleanup() hooks, and on discovery of MMCFG access we
should call the ->init() hooks?

Thanks, Roger.