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

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).


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