Re: [Xen-devel] [PATCH 2/2] IOMMU/MMU: Adjust low level functions for VT-d Device-TLB flush error.

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

On March 17, 2016 11:31pm, <George.Dunlap@xxxxxxxxxxxxx> wrote:
> On Thu, Mar 17, 2016 at 6:54 AM, Quan Xu <quan.xu@xxxxxxxxx> wrote:
> > Current code would be panic(), when VT-d Device-TLB flush timed out.
> > the panic() is going to be eliminated, so we must check all kinds of
> > error and all the way up the call trees.
> >
> > Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>
> >
> > CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> > CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> > CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> > CC: Keir Fraser <keir@xxxxxxx>
> > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> > CC: Julien Grall <julien.grall@xxxxxxx>
> > CC: Feng Wu <feng.wu@xxxxxxxxx>
> > CC: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> > ---
> >  xen/arch/x86/mm/p2m-ept.c                     |   2 +-
> >  xen/drivers/passthrough/amd/iommu_init.c      |  12 ++-
> >  xen/drivers/passthrough/amd/pci_amd_iommu.c   |   2 +-
> >  xen/drivers/passthrough/arm/smmu.c            |  10 ++-
> >  xen/drivers/passthrough/iommu.c               |  17 ++--
> >  xen/drivers/passthrough/vtd/extern.h          |   2 +-
> >  xen/drivers/passthrough/vtd/iommu.c           | 120
> ++++++++++++++++++--------
> >  xen/drivers/passthrough/vtd/quirks.c          |  26 +++---
> >  xen/include/asm-x86/hvm/svm/amd-iommu-proto.h |   2 +-
> >  xen/include/asm-x86/iommu.h                   |   2 +-
> >  xen/include/xen/iommu.h                       |   6 +-
> >  11 files changed, 133 insertions(+), 68 deletions(-)
> >
> > diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> > index f9bcce7..fa6c710 100644
> > --- a/xen/arch/x86/mm/p2m-ept.c
> > +++ b/xen/arch/x86/mm/p2m-ept.c
> > @@ -825,7 +825,7 @@ out:
> >           need_modify_vtd_table )
> >      {
> >          if ( iommu_hap_pt_share )
> > -            iommu_pte_flush(d, gfn, &ept_entry->epte, order,
> vtd_pte_present);
> > +            rc = iommu_pte_flush(d, gfn, &ept_entry->epte, order,
> > + vtd_pte_present);
> 
> So this sort changes the meaning of the "rc" check near the end of the 
> function,
> when we check whether we want to update altp2m.
> 
> As it happens, I *think* it doesn't matter, because you can't have altp2m and
> passthrough enabled at the same time, right?


I think it is _not_. 
I have gone through the altp2m design/design discussion. It looks Xen _can_ 
have altp2m and passthrough enabled at the same time.
Also you can refer to 
http://lists.xenproject.org/archives/html/xen-devel/2015-01/msg01963.html
Andrew, could you help me double check it?

> 
> If so, this at least merits a comment above the altp2m check; something like:
> 
> "NB that if altp2m is enabled, rc cannot be non-zero here due to
> iommu_pte_flush, since you can't have altp2m and pass-through enabled at the
> same time."
> 
> If you *can* have both altp2m and pass-through, then we need to make sure
> that the altp2m gets updated when the hostp2m is updated, even if the iommu
> flush fails.
> 
I think it _can_, and let's wait for the above check first.

Quan



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