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Re: [PATCH] VT-d: Tylersburg errata apply to further steppings

On Tue, Aug 03, 2021 at 03:16:14PM +0200, Jan Beulich wrote:
> On 03.08.2021 15:12, Marek Marczykowski-Górecki wrote:
> > On Tue, Aug 03, 2021 at 03:06:50PM +0200, Jan Beulich wrote:
> >> On 03.08.2021 15:01, Marek Marczykowski-Górecki wrote:
> >>> Ok, then, just setting iommu_intremap=false should do the right thing,
> >>
> >> ... if "iommu=force" is in use (but not otherwise), ...
> > 
> > But that's the purpose of iommu=force, no?
> > With "iommu=force": strictly require IOMMU
> > Without "iommu=force": use IOMMU on best-effort basis
> > 
> > It makes sense to refuse the boot if intremap is broken in the first
> > case. But also, it makes sense to allow using IOMMU without intremp in
> > the second case.
> I agree with both statements. What I disagree with is that the latter
> happens by default (instead of only upon admin override), including
> the case of intremap being unavailable in the first place.

"upon admin override" - do I read the code right, that iommu=no-intremap
will actually achieve this effect? Will that allow to use IOMMU without
interrupt remapping on a hardware where it's broken? In that case, maybe
at least add this info to the log message?

IMO an option to strictly require interrupt remapping would be useful
thing to have, but that's getting even more unrelated to this bug fix.

Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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