Re: [PATCH 06/10] vpci: Make every domain handle its own BARs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.11.2020 11:36, Julien Grall wrote:
> On 13/11/2020 10:25, Jan Beulich wrote:
>> On 13.11.2020 07:32, Oleksandr Andrushchenko wrote:
>>> On 11/12/20 4:46 PM, Roger Pau Monné wrote:
>>>> On Thu, Nov 12, 2020 at 01:16:10PM +0000, Oleksandr Andrushchenko wrote:
>>>>> On 11/12/20 11:40 AM, Roger Pau Monné wrote:
>>>>>> On Mon, Nov 09, 2020 at 02:50:27PM +0200, Oleksandr Andrushchenko wrote:
>>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>>>>> +static uint32_t bar_read_dispatch(const struct pci_dev *pdev, unsigned 
>>>>>>> int reg,
>>>>>>> +                                  void *data)
>>>>>>> +{
>>>>>>> +    struct vpci_bar *vbar, *bar = data;
>>>>>>> +
>>>>>>> +    if ( is_hardware_domain(current->domain) )
>>>>>>> +        return bar_read_hwdom(pdev, reg, data);
>>>>>>> +
>>>>>>> +    vbar = get_vpci_bar(current->domain, pdev, bar->index);
>>>>>>> +    if ( !vbar )
>>>>>>> +        return ~0;
>>>>>>> +
>>>>>>> +    return bar_read_guest(pdev, reg, vbar);
>>>>>>> +}
>>>>>>> +
>>>>>>> +static void bar_write_dispatch(const struct pci_dev *pdev, unsigned 
>>>>>>> int reg,
>>>>>>> +                               uint32_t val, void *data)
>>>>>>> +{
>>>>>>> +    struct vpci_bar *bar = data;
>>>>>>> +
>>>>>>> +    if ( is_hardware_domain(current->domain) )
>>>>>>> +        bar_write_hwdom(pdev, reg, val, data);
>>>>>>> +    else
>>>>>>> +    {
>>>>>>> +        struct vpci_bar *vbar = get_vpci_bar(current->domain, pdev, 
>>>>>>> bar->index);
>>>>>>> +
>>>>>>> +        if ( !vbar )
>>>>>>> +            return;
>>>>>>> +        bar_write_guest(pdev, reg, val, vbar);
>>>>>>> +    }
>>>>>>> +}
>>>>>> You should assign different handlers based on whether the domain that
>>>>>> has the device assigned is a domU or the hardware domain, rather than
>>>>>> doing the selection here.
>>>>> Hm, handlers are assigned once in init_bars and this function is only 
>>>>> called
>>>>>
>>>>> for hwdom, so there is no way I can do that for the guests. Hence, the 
>>>>> dispatcher
>>>> I think we might want to reset the vPCI handlers when a devices gets
>>>> assigned and deassigned.
>>>
>>> In ARM case init_bars is called too early: PCI device assignment is 
>>> currently
>>>
>>> initiated by Domain-0' kernel and is done *before* PCI devices are given 
>>> memory
>>>
>>> ranges and BARs assigned:
>>>
>>> [    0.429514] pci_bus 0000:00: root bus resource [bus 00-ff]
>>> [    0.429532] pci_bus 0000:00: root bus resource [io 0x0000-0xfffff]
>>> [    0.429555] pci_bus 0000:00: root bus resource [mem 
>>> 0xfe200000-0xfe3fffff]
>>> [    0.429575] pci_bus 0000:00: root bus resource [mem 
>>> 0x30000000-0x37ffffff]
>>> [    0.429604] pci_bus 0000:00: root bus resource [mem 
>>> 0x38000000-0x3fffffff pref]
>>> [    0.429670] pci 0000:00:00.0: enabling Extended Tags
>>> [    0.453764] pci 0000:00:00.0: -------------------- BUS_NOTIFY_ADD_DEVICE
>>>
>>> < init_bars >
>>>
>>> [    0.453793] pci 0000:00:00.0: -- IRQ 0
>>> [    0.458825] pci 0000:00:00.0: Failed to add - passthrough or MSI/MSI-X 
>>> might fail!
>>> [    0.471790] pci 0000:01:00.0: -------------------- BUS_NOTIFY_ADD_DEVICE
>>>
>>> < init_bars >
>>>
>>> [    0.471821] pci 0000:01:00.0: -- IRQ 255
>>> [    0.476809] pci 0000:01:00.0: Failed to add - passthrough or MSI/MSI-X 
>>> might fail!
>>>
>>> < BAR assignments below >
>>>
>>> [    0.488233] pci 0000:00:00.0: BAR 14: assigned [mem 
>>> 0xfe200000-0xfe2fffff]
>>> [    0.488265] pci 0000:00:00.0: BAR 15: assigned [mem 
>>> 0x38000000-0x380fffff pref]
>>>
>>> In case of x86 this is pretty much ok as BARs are already in place, but for 
>>> ARM we
>>>
>>> need to take care and re-setup vPCI BARs for hwdom.
>>
>> Even on x86 there's no guarantee that all devices have their BARs set
>> up by firmware.
>>
>> In a subsequent reply you've suggested to move init_bars from "add" to
>> "assign", but I'm having trouble seeing what this would change: It's
>> not Dom0 controlling assignment (to itself), but Xen assigns the device
>> towards the end of pci_add_device().
>>
>>> Things are getting even more
>>>
>>> complicated if the host PCI bridge is not ECAM like, so you cannot set 
>>> mmio_handlers
>>>
>>> and trap hwdom's access to the config space to update BARs etc. This is why 
>>> I have that
>>>
>>> ugly hack for rcar_gen3 to read actual BARs for hwdom.
>>
>> How to config space accesses work there? The latest for MSI/MSI-X it'll
>> be imperative that Xen be able to intercept config space writes.
> 
> I am not sure to understand your last sentence. Are you saying that we 
> always need to trap access to MSI/MSI-X message in order to sanitize it?
> 
> If one is using the GICv3 ITS (I haven't investigated other MSI 
> controller), then I don't believe you need to sanitize the MSI/MSI-X 
> message in most of the situation.

Well, if it's fine for the guest to write arbitrary values to message
address and message data, _and_ to arbitrarily enable/disable MSI / MSI-X,
then yes, no interception would be needed.

Jan