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 8:34pm, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> On Thu, Mar 17, 2016 at 12:30 PM, George Dunlap
> <George.Dunlap@xxxxxxxxxxxxx> 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()?
> >
> >>      return rc;
> >>  }
> >>
> >> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> >> index 3cb6868..f9bcce7 100644
> >> --- a/xen/arch/x86/mm/p2m-ept.c
> >> +++ b/xen/arch/x86/mm/p2m-ept.c
> >> @@ -830,7 +830,15 @@ out:
> >>          {
> >>              if ( iommu_flags )
> >>                  for ( i = 0; i < (1 << order); i++ )
> >> -                    iommu_map_page(d, gfn + i, mfn_x(mfn) + i,
> iommu_flags);
> >> +                {
> >> +                    rc = iommu_map_page(d, gfn + i, mfn_x(mfn) + i,
> iommu_flags);
> >> +                    if ( rc )
> >> +                    {
> >> +                        while ( i-- > 0 )
> >> +                            iommu_unmap_page(d, gfn + i);
> >
> > This won't unmap gfn+0 (since it will break out when i == 0 without
> > calling unmap).
> 
> Oh, no it won't, because the decrement is postfix.
> 
> For us mere mortals, I'd appreciate a comment here like this:
> 
> /* Postfix operator means we will call unmap with i == 0 */
> 
Agreed.
For these 2 points, to summarize:
   - adding "unlikely()" to the if() condition, e.g. if ( unlikely(rc) )
   - adding a comment:
        /* Postfix operator means we will call unmap with i == 0 */


Right?

Quan

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