On 10.12.10 at 19:26, "Kay, Allen M" <allen.m.kay@xxxxxxxxx> wrote:
The architectural requirement is actually between interrupt remapping and
x2apic. Since interrupt remapping is part of the VT-d feature so current
software requires all VT-d features enabled in order for x2apic to be enabled.
Strictly speaking DMA remapping is not required for x2apic. However, queued
invalidation is required since interrupt remapping requires queued
invalidation. So x2apic dependency is as follows:
x2apic->interrupt remapping->queued invalidation
Due to historical reasons, the new VT-d features were built on top of the old
ones as they become available. Is there a requirement to separate this out?
If so, we will need to re-design iommu boot parameter which took a while to
get it right so most systems can now boot successfully.
And why is it that Xen panics when the BIOS pre-enabled x2apic
mode without also enabling interrupt re-mapping, while Linux
(afaict from looking at 2.6.32 code and output from an affected
machine) simply enables interrupt re-mapping in this case?
Thanks, Jan