Re: [Xen-devel] [PATCH v9 2/3] VT-d: wrap a _sync version for all VT-d flush interfaces

["Xu, Quan" <quan.xu@xxxxxxxxx>]

On April 07, 2016 11:29pm, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >>> On 07.04.16 at 09:44, <quan.xu@xxxxxxxxx> wrote:
> > On April 05, 2016 5:35pm, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >> >>> On 01.04.16 at 16:47, <quan.xu@xxxxxxxxx> wrote:
> >> > +{
> >> > +    queue_invalidate_context(iommu, did, source_id,
> >> > +                             function_mask, granu);
> >> > +
> >> > +    return invalidate_sync(iommu); }
> >>
> >> Further down you replace the only call to
> >> queue_invalidate_context() - why keep both functions instead of just
> >> making
> > the
> >> existing one do the sync? (That would the likely also apply to
> >> qinval_device_iotlb() and others below.)
> >>
> >
> > It is optional.
> >  I think:
> > 1. in the long term, we may need no _sync version.
> > 2. At least, the current wrap looks good to me. e.g.
> > queue_invalidate_context() is for context-cache Invalidate Descriptor,
> > and the
> > invalidate_sync() is for Invalidation Wait Descriptor. It is much clearer.
> 
> I don't really agree, but will leave it to the VT-d maintainers to judge.
> 

+to Kevin and Feng, I am open for it.


> >> > +        if ( ret )
> >> > +            return ret;
> >> > +
> >> >          if ( flush_dev_iotlb )
> >> >              ret = dev_invalidate_iotlb(iommu, did, addr, size_order,
> type);
> >> > -        rc = invalidate_sync(iommu);
> >> > -        if ( !ret )
> >> > -            ret = rc;
> >> >      }
> >>
> >> I think leaving the existing logic as is would be better - best
> >> effort
> > invalidation
> >> even when an error has occurred.
> >>
> >
> > I have an open:
> > As vt-d spec(:Queued Invalidation Ordering Considerations) said,
> >      1. If the Fence(FN) flag is 1 in a inv_wait_dsc, hardware must
> > execute descriptors following the inv_wait_dsc only after wait command is
> completed.
> >      2. when a Device-TLB invalidation timeout is detected, hardware
> > must not complete any pending inv_wait_dsc commands.
> > In current code, the Fence(FN) is always 1.
> > if a Device-TLB invalidation timeout is detected, this additional
> > inv_wait_dsc is not completed.
> > __iiuc__,
> > the new coming descriptors, in that queue, _might_ be not executed any
> > more, waiting for this additional inv_wait_dsc which is not completed.
> > is it true?
> 
> That's not a question to me, is it?

To community, but vt-d maintainers are someone who can explain to me.

Quan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel