Re: [Xen-devel] GPU passthrough performance regression in >4GB vms due to XSA-60 changes

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.05.14 at 13:18, <tomasz.wroblewski@xxxxxxxxx> wrote:
>> If I coded up a patch to deal with this on -unstable, would you be
>> able to test that?
> Willing to give it a go (xen major version updates are often problematic 
> to do though so can't promise success). What would your patch be doing? 
> Adding entries to MTRR for the relocated regions?

This and properly declare the region in ACPI's _CRS. For starters I'll
probably try keeping the WB default overlaid with UC variable ranges,
as that's going to be the less intrusive change.

> I do fear it might not 
> be enough since thru recent debugging it seems there are more wrongs 
> done by the relocation code - the p2m entries for the relocated region 
> are not setup with p2m_mmio_direct for example but rather default 
> p2m_ram_rw (unless this has changed again past 4.3.2).

Hmm, I would hope that's not a problem anymore on -unstable, but
then again I neither recall a change nor am I sure where this would
go wrong (in the hypervisor - all it cares about is that the tools
properly invoke XEN_DOMCTL_memory_mapping; please check that
these calls are being made).

Jan


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