Re: [PATCH v7 5/7] xen/arm: do not map PCI ECAM and MMIO space to Domain-0's p2m

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

Hi, Julien!

On 08.12.21 19:20, Julien Grall wrote:
> Hi Oleksandr,
>
> On 24/11/2021 07:59, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>
>> PCI host bridges are special devices in terms of implementing PCI
>> passthrough. According to [1] the current implementation depends on
>> Domain-0 to perform the initialization of the relevant PCI host
>> bridge hardware and perform PCI device enumeration. In order to
>> achieve that one of the required changes is to not map all the memory
>> ranges in map_range_to_domain as we traverse the device tree on startup
>> and perform some additional checks if the range needs to be mapped to
>> Domain-0.
>>
>> The generic PCI host controller device tree binding says [2]:
>> - ranges: As described in IEEE Std 1275-1994, but must provide
>>            at least a definition of non-prefetchable memory. One
>>            or both of prefetchable Memory and IO Space may also
>>            be provided.
>>
>> - reg   : The Configuration Space base address and size, as accessed
>>            from the parent bus.  The base address corresponds to
>>            the first bus in the "bus-range" property.  If no
>>            "bus-range" is specified, this will be bus 0 (the default).
>>
>>  From the above none of the memory ranges from the "ranges" property
>> needs to be mapped to Domain-0 at startup as MMIO mapping is going to
>> be handled dynamically by vPCI as we assign PCI devices, e.g. each
>> device assigned to Domain-0/guest will have its MMIOs mapped/unmapped
>> as needed by Xen.
>>
>> The "reg" property covers not only ECAM space, but may also have other
>> then the configuration memory ranges described, for example [3]:
>> - reg: Should contain rc_dbi, config registers location and length.
>> - reg-names: Must include the following entries:
>>     "rc_dbi": controller configuration registers;
>>     "config": PCIe configuration space registers.
>>
>> This patch makes it possible to not map all the ranges from the
>> "ranges" property and also ECAM from the "reg". All the rest from the
>> "reg" property still needs to be mapped to Domain-0, so the PCI
>> host bridge remains functional in Domain-0. This is done by first
>> skipping the mappings while traversing the device tree as it is done for
>> usual devices and then by calling a dedicated pci_host_bridge_mappings
>> function which only maps MMIOs required by the host bridges leaving the
>> regions, needed for vPCI traps, unmapped.
>>
>> [1] 
>> https://lists.xenproject.org/archives/html/xen-devel/2020-07/msg00777.html
>> [2] 
>> https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/host-generic-pci.txt
>> [3] 
>> https://www.kernel.org/doc/Documentation/devicetree/bindings/pci/hisilicon-pcie.txt
>>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>
> Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
>
> I haven't committed because it is not clear whether this patch depends on 
> earlier patches that are still under review. Can you advise?
I will resend the whole series (leftovers), so no need to commit now

Thank you,
Oleksandr
>
> Cheers,
>