Re: [Xen-devel] [PATCH v2] x86 / iommu: set up a scratch page in the quarantine domain

[Jürgen Groß <jgross@xxxxxxxx>]

On 10.12.19 09:57, Jan Beulich wrote:
> On 10.12.2019 09:12, Jürgen Groß wrote:
> > On 10.12.19 09:05, Jan Beulich wrote:
> > > On 10.12.2019 08:16, Tian, Kevin wrote:
> > > > While the quarantine idea sounds good overall, I'm still not convinced
> > > > to have it the only way in place just for handling some known-buggy
> > > > device. It kills the possibility of identifying a new buggy device and then
> > > > deciding not to use it in the first space... I thought about whether it
> > > > will get better when future IOMMU implements A/D bit - by checking
> > > > access bit being set then we'll know some buggy device exists, but,
> > > > the scratch page is shared by all devices then we cannot rely on this
> > > > feature to find out the actual buggy one.
> > > Thinking about it - yes, I think I agree. This (as with so many
> > > workarounds) would better be an off-by-default one. The main issue
> > > I understand this would have is that buggy systems then might hang
> > > without even having managed to get a log message out - Paul?
> > >
> > > Jürgen - would you be amenable to an almost last minute refinement
> > > here (would then also need to still be backported to 4.12.2, or
> > > the original backport reverted, to avoid giving the impression of
> > > a regression)?
> > So what is your suggestion here? To have a boot option (defaulting to
> > off) for enabling the scratch page?
> Yes (and despite having seen Paul's reply).
I'd release ack such a patch in case you come to an agreement regarding
the default soon.


Juergen

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