Re: [Xen-devel] [PATCH 1/2] IOMMU/MMU: Adjust top level functions for VT-d Device-TLB flush error.

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

On March 17, 2016 8:30pm, <dunlapg@xxxxxxxxx> wrote:
> On Thu, Mar 17, 2016 at 6:54 AM, Quan Xu <quan.xu@xxxxxxxxx> wrote:
> > diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index
> > c997b53..526548e 100644
> > --- a/xen/arch/x86/mm.c
> > +++ b/xen/arch/x86/mm.c
> > @@ -2467,7 +2467,7 @@ static int __get_page_type(struct page_info *page,
> unsigned long type,
> >                             int preemptible)  {
> >      unsigned long nx, x, y = page->u.inuse.type_info;
> > -    int rc = 0;
> > +    int rc = 0, ret = 0;
> >
> >      ASSERT(!(type & ~(PGT_type_mask | PGT_pae_xen_l2)));
> >
> > @@ -2578,11 +2578,11 @@ static int __get_page_type(struct page_info
> *page, unsigned long type,
> >          if ( d && is_pv_domain(d) && unlikely(need_iommu(d)) )
> >          {
> >              if ( (x & PGT_type_mask) == PGT_writable_page )
> > -                iommu_unmap_page(d, mfn_to_gmfn(d,
> page_to_mfn(page)));
> > +                ret = iommu_unmap_page(d, mfn_to_gmfn(d,
> page_to_mfn(page)));
> >              else if ( type == PGT_writable_page )
> > -                iommu_map_page(d, mfn_to_gmfn(d,
> page_to_mfn(page)),
> > -                               page_to_mfn(page),
> > -
> IOMMUF_readable|IOMMUF_writable);
> > +                ret = iommu_map_page(d, mfn_to_gmfn(d,
> page_to_mfn(page)),
> > +                                     page_to_mfn(page),
> > +
> IOMMUF_readable|IOMMUF_writable);
> >          }
> >      }
> >
> > @@ -2599,6 +2599,9 @@ static int __get_page_type(struct page_info *page,
> unsigned long type,
> >      if ( (x & PGT_partial) && !(nx & PGT_partial) )
> >          put_page(page);
> >
> > +    if ( !rc )
> > +        rc = ret;
> > +
> 
> What's this about?  If the iommu_[un]map_page() operation times out,
> we still go through with calling alloc_page_type(); and if
> alloc_page_type() fails we return its failure value, but if it
> succeeds, we return the error from iommu_[un]map_page()?
> 
Yes.
To be honest, to me, it is tricky too. 
I found it is not right to return directly if the iommu_[un]map_page() 
operation times out.

 """if ( d && is_pv_domain(d) && unlikely(need_iommu(d)) )"""
Does IOMMU support pv domain? If not, we'd better remove the " if(...){...}"

Quan


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