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Re: [Xen-devel] [PATCH] VTD/Intremap: Disable Intremap on Chipset 5500/5520/X58 due to errata

On 16/01/13 14:14, Jan Beulich wrote:
On 16.01.13 at 00:27, Malcolm Crossley <malcolm.crossley@xxxxxxxxxx> wrote:
Unfortunately this chipset is very common and many BIOSes are not
disabling remapping.  We can detect this in Xen and prevent turning on
remapping in the first place.  However, this will turn VT-d off on many
systems by default.
Why would the IOMMU be turned off in that case as a whole?
Interrupt remapping is not a prerequisite iirc.
You are correct. I read the description of XSA-3 but didn't the check the current xen-unstable code correctly.
Users who still wish to use VT-d can use iommu=force if they are happy
exposing the associated security risk.
"iommu=force" doesn't enable interrupt remapping if it was
forcibly turned off.
This was based upon the faulty code reading above and therefore the comment is wrong . I will change the patch description.

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