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

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

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 */

Thanks,
 -George

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