On 2025/7/21 22:16, Roger Pau Monné wrote:
> On Wed, Jul 09, 2025 at 05:34:28AM +0000, Chen, Jiqian wrote:
>> 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.
>
> Hm, I see the asymmetry of allowing writes but not direct writes, my
> thought was to give the hw domain as less interference as possibly,
> hence my recommendation to use vpci_hw_write32().
>
> I practice I think it's very unlikely that devices re-use reserved
> bits in the capability register, so I'm fine with using NULL (thus
> discarding the write). We can always add more complex handling here
> if we ever came across a device that requires it.
OK, I will delete vpci_hw_write32() in next version.
Thanks.
>
> Thanks, Roger.
--
Best regards,
Jiqian Chen.
