Re: [PATCH v7 1/8] vpci/header: Emulate extended capability list for dom0

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2025/7/9 13:32, Jan Beulich wrote:
> On 09.07.2025 07:29, Chen, Jiqian wrote:
>> On 2025/7/8 22:10, Jan Beulich wrote:
>>> On 04.07.2025 09:07, Jiqian Chen wrote:
>>>> --- a/xen/drivers/vpci/header.c
>>>> +++ b/xen/drivers/vpci/header.c
>>>> @@ -836,6 +836,39 @@ static int vpci_init_capability_list(struct pci_dev 
>>>> *pdev)
>>>>                                    PCI_STATUS_RSVDZ_MASK);
>>>>  }
>>>>  
>>>> +static int vpci_init_ext_capability_list(const struct pci_dev *pdev)
>>>> +{
>>>> +    unsigned int pos = PCI_CFG_SPACE_SIZE;
>>>> +
>>>> +    if ( !is_hardware_domain(pdev->domain) )
>>>> +        /* Extended capabilities read as zero, write ignore for DomU */
>>>> +        return vpci_add_register(pdev->vpci, vpci_read_val, NULL,
>>>> +                                 pos, 4, (void *)0);
>>>> +
>>>> +    do
>>>> +    {
>>>> +        uint32_t header = pci_conf_read32(pdev->sbdf, pos);
>>>> +        int rc;
>>>> +
>>>> +        rc = vpci_add_register(pdev->vpci, vpci_read_val, vpci_hw_write32,
>>>> +                               pos, 4, (void *)(uintptr_t)header);
>>>
>>> If it wasn't for this use of vpci_hw_write32(), I'd be happy to provide my
>>> R-b. But this continues to look bogus to me: What use is it to allow writes
>>> when Dom0 then can't read back any possible effect of such a write (in the
>>> unexpected event that some of the bits were indeed writable)?
>> Oh, I got your concern.
>> What do you think about updating the header value after writing to hardware 
>> in write function?
> 
> That would imo be a layering violation. Once again that's something that you
> primarily would need Roger's input on.
OK, wait for Roger's input.

> 
>> Or you prefer to pass NULL here?
> 
> Yes, that's what I've been trying to argue for.
> 
> Jan

-- 
Best regards,
Jiqian Chen.