On 8/31/23 08:11, Jan Beulich wrote:
> On 28.08.2023 19:56, Stewart Hildebrand wrote:
>> Currently, Xen vPCI only supports virtualizing the MSI and MSI-X
>> capabilities.
>> Hide all other PCI capabilities (including extended capabilities) from domUs
>> for
>> now, even though there may be certain devices/drivers that depend on being
>> able
>> to discover certain capabilities.
>>
>> We parse the physical PCI capabilities linked list and add vPCI register
>> handlers for the next elements, inserting our own next value, thus
>> presenting a
>> modified linked list to the domU.
>>
>> Introduce helper functions vpci_hw_read8 and vpci_read_val. The vpci_read_val
>> helper function returns a fixed value, which may be used for RAZ registers,
>> or
>> registers whose value doesn't change.
>>
>> Introduce pci_find_next_cap_ttl() helper while adapting the logic from
>> pci_find_next_cap() to suit our needs, and implement the existing
>> pci_find_next_cap() in terms of the new helper.
>>
>> Signed-off-by: Stewart Hildebrand <stewart.hildebr...@amd.com>
>
> Reviewed-by: Jan Beulich <jbeul...@suse.com>>
> Nevertheless a couple of remarks:
>
>> --- a/xen/drivers/pci/pci.c
>> +++ b/xen/drivers/pci/pci.c
>> @@ -39,31 +39,44 @@ unsigned int pci_find_cap_offset(pci_sbdf_t sbdf,
>> unsigned int cap)
>> return 0;
>> }
>>
>> -unsigned int pci_find_next_cap(pci_sbdf_t sbdf, unsigned int pos,
>> - unsigned int cap)
>> +unsigned int pci_find_next_cap_ttl(pci_sbdf_t sbdf, unsigned int pos,
>> + bool (*is_match)(unsigned int, unsigned
>> int),
>> + unsigned int userdata, unsigned int *ttl)
>> {
>> - u8 id;
>> - int ttl = 48;
>> + unsigned int id;
>>
>> - while ( ttl-- )
>> + while ( (*ttl)-- )
>> {
>> pos = pci_conf_read8(sbdf, pos);
>> if ( pos < 0x40 )
>> break;
>>
>> - pos &= ~3;
>> - id = pci_conf_read8(sbdf, pos + PCI_CAP_LIST_ID);
>> + id = pci_conf_read8(sbdf, (pos & ~3) + PCI_CAP_LIST_ID);
>>
>> if ( id == 0xff )
>> break;
>> - if ( id == cap )
>> + if ( is_match(id, userdata) )
>> return pos;
>>
>> - pos += PCI_CAP_LIST_NEXT;
>> + pos = (pos & ~3) + PCI_CAP_LIST_NEXT;
>> }
>> +
>> return 0;
>> }
>>
>> +static bool cf_check is_cap_match(unsigned int id1, unsigned int id2)
>> +{
>> + return id1 == id2;
>> +}
>
> Personally I would have preferred to get away without yet another hook
> function here, by ...
>
>> +unsigned int pci_find_next_cap(pci_sbdf_t sbdf, unsigned int pos,
>> + unsigned int cap)
>> +{
>> + unsigned int ttl = 48;
>> +
>> + return pci_find_next_cap_ttl(sbdf, pos, is_cap_match, cap, &ttl) & ~3;
>
> ... passing NULL here and then suitably handling the case in that
> common helper.
Thinking in terms of reducing the amount of dead code, I'll change it
>> @@ -561,6 +573,71 @@ static int cf_check init_bars(struct pci_dev *pdev)
>> if ( rc )
>> return rc;
>>
>> + if ( !is_hardware_domain(pdev->domain) )
>> + {
>> + if ( !(pci_conf_read16(pdev->sbdf, PCI_STATUS) &
>> PCI_STATUS_CAP_LIST) )
>> + {
>> + /* RAZ/WI */
>> + rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL,
>> + PCI_CAPABILITY_LIST, 1, (void *)0);
>> + if ( rc )
>> + return rc;
>> + }
>> + else
>> + {
>> + /* Only expose capabilities to the guest that vPCI can handle.
>> */
>> + uint8_t next;
>
> If this was "unsigned long", ...
>
>> + unsigned int ttl = 48;
>> +
>> + next = pci_find_next_cap_ttl(pdev->sbdf, PCI_CAPABILITY_LIST,
>> + vpci_cap_supported, 0, &ttl);
>> +
>> + rc = vpci_add_register(pdev->vpci, vpci_read_val, NULL,
>> + PCI_CAPABILITY_LIST, 1,
>> + (void *)(uintptr_t)next);
>
> ... you'd avoid the need for the double cast here and again below. Yet
> then I realize that Misra would take offence at us doing so ...
As ugly as that double cast is, I think I prefer the next and pos declarations
have consistent types (which I had intended to be unsigned int to match the
prior patches, not uint8_t). As well as not making the MISRA situation any
worse. The casts, after all, make it excruciatingly obvious what we're doing
here, I hope.
Stew
