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

[Paul Durrant <xadimgnik@xxxxxxxxx>]

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