Re: [RFC PATCH] iommu: make no-quarantine mean no-quarantine

[Paul Durrant <xadimgnik@gmail.com>]

On 28/04/2021 09:49, Jan Beulich wrote:
> On 28.04.2021 09:19, Paul Durrant wrote:
>> On 28/04/2021 07:15, Jan Beulich wrote:
>>> Following the extension to the command line option I'm putting in place
>>> in "IOMMU: make DMA containment of quarantined devices optional" (which
>>> I still need to get around to address review feedback for and resubmit),
>>> I'd be inclined to suggest "iommu=quarantine=always" or
>>> "iommu=quarantine=on-assign". Unless of course we'd prefer to have the
>>> caller of the assignment operation have full control over the behavior
>>> here anyway (in which case a command line option control simply is not
>>> necessary).
>>>
>>
>> I'm still not entirely sure why not quarantining on is a problem,
> 
> Well, I continue to think that it is a mistake to hide problems (with
> their hardware) from system administrators by default. I guess most
> everyone else put usability in foreground, as my view to workarounds
> (with non-benign [side-]effects) being enabled by default looks to be
> generally different.
> 
>> other
>> than it triggering an as-yet undiagnosed issue in QEMU, but I agree that
>> that the expectation of 'no-quarantine' meaning just that (i.e. the old
>> dom0->domU and domU->dom0 transitions are re-instated) is reasonable.
> 
> I'm afraid I'm not clear what you're talking about here. What "old
> transitions"? The ones prior to the introduction of quarantining?

FAOD, that's what I meant.

   Paul

> If
> so, and if the tool stack is given (some level of) control, I guess
> we'd first need to establish who "rules": The command line option,
> or the tool stack (which imo ought to be acting whichever particular
> way based on admin requests, not to blindly override Xen's defaults).
> 
>> Do we really want yet more command line options?
> 
> If we can avoid them without sacrificing functionality / flexibility ...
> 
> Jan
>