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

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.


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