Re: [Xen-devel] [PATCH v2 3/3] OvmfPkg/XenSupport: turn off address decoding before BAR sizing

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 11/04/2019 15:13, Igor Druzhinin wrote:
> On 11/04/2019 14:19, Andrew Cooper wrote:
>> On 09/04/2019 04:12, Igor Druzhinin wrote:
>>> On Xen, hvmloader firmware leaves address decoding enabled for
>>> enumerated PCI device before jumping into OVMF. OVMF seems to
>>> expect it to be disabled and tries to size PCI BARs in several places
>>> without disabling it which causes BAR64, for example, being
>>> incorrectly placed by QEMU.
>>>
>>> Fix it by disabling PCI address decoding explicitly before the
>>> first attempt to size BARs on Xen.
>>
>> This is an HVMLoader bug, surely?
> 
> I'll try to turn it off in HVMLoader but I'm not sure other BIOSes would
> like it. Although they should not make any assumptions on whether memory
> decoding is enabled or not (so as OVMF - hence this patch) it's still
> risky from my point of view.

Having tested ROMBIOS and SeaBIOS - none of them worked without
hvmloader enabling decoding. While it seems wrong - they obviously
plagued by the same assumption on system state as OVMF. This patch
addresses the issue in OVMF and I think that's correct. Addressing the
issue in other BIOSes might be considered an improvement for the future.

Igor

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