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

[Julien Grall <julien@xen.org>]

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@epam.com>
>>>>>> +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.

Cheers,

-- 
Julien Grall