Re: [Xen-devel] [PATCH] IOMMU/x86: avoid pages without GFN in page table creation/updating

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.05.15 at 04:53, <yang.z.zhang@xxxxxxxxx> wrote:
> Jan Beulich wrote on 2015-05-07:
>> --- a/xen/drivers/passthrough/x86/iommu.c
>> +++ b/xen/drivers/passthrough/x86/iommu.c
>> @@ -59,10 +59,17 @@ int arch_iommu_populate_page_table(struc
>>          if ( has_hvm_container_domain(d) ||
>>              (page->u.inuse.type_info & PGT_type_mask) ==
>> PGT_writable_page )
>>          {
>> -            BUG_ON(SHARED_M2P(mfn_to_gmfn(d,
>> page_to_mfn(page))));
>> -            rc = hd->platform_ops->map_page(
>> -                d, mfn_to_gmfn(d, page_to_mfn(page)),
>> page_to_mfn(page),
>> -                IOMMUF_readable|IOMMUF_writable);
>> +            unsigned long mfn = page_to_mfn(page);
>> +            unsigned long gfn = mfn_to_gmfn(d, mfn);
>> +
>> +            if ( gfn != INVALID_MFN )
>> +            {
>> +                ASSERT(!(gfn >> DEFAULT_DOMAIN_ADDRESS_WIDTH));
>> +                BUG_ON(SHARED_M2P(gfn));
> 
> It seems ASSERT() is unnecessary. BUG_ON() is enough to cover it.

The two check completely different things, so I don't see how
the BUG_ON() would help with out of bounds, yet also not
INVALID_MFN GFNs. Please clarify what you mean here.

Jan


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