Re: [Xen-devel] [PATCH] x86/ats: Disable Address Translation Services by default

[Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>]

Andrew/Jan,

I have verified that PCI device pass-through works with ATS disabled. 
Although, could you please help described how "asynchronous queued 
invalidation support" supposed to work?
Thanks,

Suravee

On 08/22/2014 07:39 AM, Jan Beulich wrote:
> > > > On 20.08.14 at 18:01, <andrew.cooper3@xxxxxxxxxx> wrote:
> > Xen cannot safely use any ATS functionality until it gains asynchronous
> > queued
> > invalidation support, because of the current synchronous wait for
> > completion.
> >
> > Do not turn ATS on by default.
> >
> > While editing the default in the command line documentation, correct the
> > statement regarding PCI Passthrough.  ATS is purely a performance
> > optimisation, and is certainly not required for PCI Passthrough to function.
> >
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > CC: Jan Beulich <JBeulich@xxxxxxxx>
> Even if not mandated by ./MAINTAINERS I think this definitely
> should have been Cc-ed to the VT-d and AMD IOMMU maintainers
> (now done).
>
> Jan
>
> > ---
> >   docs/misc/xen-command-line.markdown |    9 ++++++---
> >   xen/drivers/passthrough/x86/ats.c   |    2 +-
> >   2 files changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/docs/misc/xen-command-line.markdown
> > b/docs/misc/xen-command-line.markdown
> > index a8cab59..5f4680f 100644
> > --- a/docs/misc/xen-command-line.markdown
> > +++ b/docs/misc/xen-command-line.markdown
> > @@ -176,10 +176,13 @@ developers wishing Xen to fall back to older timing
> > methods on newer hardware.
> >   ### ats
> >   > `= <boolean>`
> >
> > -> Default: `true`
> > +> Default: `false`
> > +
> > +Permits Xen to set up and use PCI Address Translation Services.  This is a
> > +performance optimisation for PCI Passthrough.
> >
> > -Permits Xen to set up and use PCI Address Translation Services, which
> > -is required for PCI Passthrough.
> > +**WARNING: Xen cannot currently safely use ATS because of its synchronous
> > wait
> > +loops for Queued Invalidation completions.**
> >
> >   ### availmem
> >   > `= <size>`
> > diff --git a/xen/drivers/passthrough/x86/ats.c
> > b/xen/drivers/passthrough/x86/ats.c
> > index 1e3e03a..436eada 100644
> > --- a/xen/drivers/passthrough/x86/ats.c
> > +++ b/xen/drivers/passthrough/x86/ats.c
> > @@ -20,7 +20,7 @@
> >
> >   LIST_HEAD(ats_devices);
> >
> > -bool_t __read_mostly ats_enabled = 1;
> > +bool_t __read_mostly ats_enabled = 0;
> >   boolean_param("ats", ats_enabled);
> >
> >   int enable_ats_device(int seg, int bus, int devfn, const void *iommu)
> > --
> > 1.7.10.4
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