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

[Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>]

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.
> Jan

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