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

["Durrant, Paul" <pdurrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Tian, Kevin <kevin.tian@xxxxxxxxx>
> Sent: 25 November 2019 08:22
> To: Durrant, Paul <pdurrant@xxxxxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Roger Pau Monné
> <roger.pau@xxxxxxxxxx>
> Subject: RE: [PATCH] x86 / iommu: set up a scratch page in the quarantine
> domain
> 
> > From: Paul Durrant [mailto:pdurrant@xxxxxxxxxx]
> > Sent: Wednesday, November 20, 2019 8:09 PM
> >
> > This patch introduces a new iommu_op to facilitate a per-implementation
> > quarantine set up, and then further code for x86 implementations
> > (amd and vtd) to set up a read/wrote scratch page to serve as the
> source/
> > target for all DMA whilst a device is assigned to dom_io.
> >
> > The reason for doing this is that some hardware may continue to re-try
> > DMA, despite FLR, in the event of an error. Having a scratch page mapped
> > will allow pending DMA to drain and thus quiesce such buggy hardware.
> 
> then there is no diagnostics at all since all faults are quiescent now...
> why do we want to support such buggy hardware? Is it better to make
> it an default-off option since buggy is supposed to niche case?

I guess it could be a command line option... perhaps making the new 
'iommu=quarantine' boolean into something more complex, but I'm not sure it's 
really worth it. Perhaps a compile time option would be better?

  Paul
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