Re: [PATCH v2 3/8] vpci/header: Emulate extended capability list for host

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

On Wed, Apr 09, 2025 at 02:45:23PM +0800, Jiqian Chen wrote:
> Add a new function to emulate extended capability list for host,
> and call it in init_header(). So that, it will be easy to hide
> a capability whose initialization fails.
> 
> As for the extended capability list of guest, keep hiding it.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
> cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> ---
> v1->v2 changes:
> new patch
> 
> Best regards,
> Jiqian Chen.
> ---
>  xen/drivers/vpci/header.c | 44 ++++++++++++++++++++++++++++++++-------
>  1 file changed, 36 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
> index 0910eb940e23..6833d456566b 100644
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -815,6 +815,39 @@ static int vpci_init_capability_list(struct pci_dev 
> *pdev)
>      return rc;
>  }
>  
> +static int vpci_init_ext_capability_list(struct pci_dev *pdev)
> +{
> +    int rc;
> +    u32 header;

uint32_t would be preferred.

> +    unsigned int pos = 0x100U, ttl = 480;
> +
> +    if ( !is_hardware_domain(pdev->domain) )
> +    {
> +        /* Extended capabilities read as zero, write ignore */
> +        rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL,
> +                               pos, 4, (void *)0);
> +        if ( rc )
> +            return rc;

I think you want to unconditionally return here, otherwise you will
most likely add a duplicated handler over "pos" when going inside the
loop below?

Also for domU we don't want to expose any extended capabilities yet.

> +    }
> +
> +    while ( pos && ttl-- )
> +    {
> +        header = pci_conf_read32(pdev->sbdf, pos);
> +
> +        rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL,

You don't want to pass NULL here, as that would prevent dom0 from
writing to the register, you instead want to pass vpci_hw_write32 I
think.

> +                               pos, 4, (void *)(uintptr_t)header);
> +        if ( rc )
> +            return rc;
> +
> +        if ( (header == 0) || (header == -1) )
> +            return 0;
> +
> +        pos = PCI_EXT_CAP_NEXT(header);

Don't you need to check that pos >= 0x100?  Possibly done in the while
loop condition: while ( pos >= 0x100 && ... )

Thanks, Roger.