Re: [PATCH 4/4] thunderbolt: Export IOMMU based DMA protection support to userspace

[Yehezkel Bernat <yehezkelshb@gmail.com>]

On Tue, Nov 13, 2018 at 12:56 PM Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
>
> > Just one point:
> > Have you considered the option to add this property per (TBT?) device?
>
> No. ;-)
>
> You mean that one device uses security levels and another IOMMU? I don't
> think it is possible without having some sort of table in the IOMMU
> driver telling which devices it needs identity map and which not. Also
> not sure what would be the benefit?

For performance, of course. If some devices are considered safe (maybe a list
communicated by platform firmware), the kernel may decide to configure them to
passthrough the IOMMU (I think I remember there is such an option, but maybe I'm
wrong.)


> > If the kernel may decide to enable/disable the IOMMU or AST per device, maybe
> > it should be on this level.
> > Or maybe the IOMMU decision isn't going to change (it's system-wide) and the AST
> > decision will be communicated per device by a new sysfs attribute anyway, if
> > needed?
>
> Not sure what you mean by "AST"? The IOMMU decision is pretty much
> system-wide.

Sorry, I meant ATS, Address Translation Service, mentioned in patch 3 in this
series, and possibly be enabled for some devices for performance, as mentioned
there.
So if needed, this will be another attribute, and definitely
per-device, isn't it?