Re: [Xen-devel] [BUG] After upgrade to Xen 4.12.0 iommu=no-igfx

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

De-htmling...

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[snip]
For RMRRs themselves, system firmware is well known for abiding by the spec 
[citation needed], but an RMRR must be honoured, because the entire purpose of 
them is to state "this device won't function without access to this area".

An RMRR in a hole, while a violation of the spec, is obviously fine to use in 
practice, so we should just accept it and stop complaining.

OTOH, RMRRs which hit other memory (particularly RAM) need more care, and 
probably want to force override the e820 to reserved.  Nothing good will come 
from trusting the e820 over the DMAR table here, seeing as there is clearly an 
error somewhere in the firmware-provided information.

However - I'm struggling to locate anywhere which actually walks dom0's RMRR 
list and inserts them into the IOMMU.  Anyone got any hints?
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I think you want setup_hwdom_rmrr() in passthrough/vtd/iommu.c

  Paul
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