[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH] xen/pci: try to reserve MCFG areas earlier



On 08/09/2019 19:28, Boris Ostrovsky wrote:
> On 9/6/19 7:00 PM, Igor Druzhinin wrote:
>>
>> On 06/09/2019 23:30, Boris Ostrovsky wrote:
>>>
>>> Where is MCFG parsed? pci_arch_init()?
>>>> It happens twice:
>> 1) first time early one in pci_arch_init() that is arch_initcall - that
>> time pci_mmcfg_list will be freed immediately there because MCFG area is
>> not reserved in E820;
>> 2) second time late one in acpi_init() which is subsystem_initcall right
>> before where PCI enumeration starts - this time ACPI tables will be
>> checked for a reserved resource and pci_mmcfg_list will be finally
>> populated.
>>
>> The problem is that on a system that doesn't have MCFG area reserved in
>> E820 pci_mmcfg_list is empty before acpi_init() and our PCI hooks are
>> called in the same place. So MCFG is still not in use by Xen at this
>> point since we haven't reached our xen_mcfg_late().
> 
> 
> Would it be possible for us to parse MCFG ourselves in pci_xen_init()? I
> realize that we'd be doing this twice (or maybe even three times since
> apparently both pci_arch_init()  and acpi_ini() do it).
> 

I don't thine it makes sense:
a) it needs to be done after ACPI is initialized since we need to parse
it to figure out the exact reserved region - that's why it's currently
done in acpi_init() (see commit message for the reasons why)
b) given (a) we cannot do it ourselves before acpi_init and after is too
late as we're already past ACPI PCI enumeration
c) we'd have to do it in the same place I call xen_mcfg_late() and it'd
be code duplication of what's already done by the existing code.

Igor

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.