Re: [PATCH 1/1] x86/iommu: fix dma pte address size error

[Li, Zhen-Hua (USL-China)]

Hi Don,

This patch is not only for the sake of spec interpretation.
Till now I did not see any bugs , but it does not meant no bugs will appear
in the future. The address returned by dma_pte_addr is used in many places.

Thanks
Zhenhua


On 06/15/2013 04:16 AM, Don Dutile wrote:
> On 05/23/2013 08:35 PM, Li, Zhen-Hua wrote:
> > In Intel Vt-D specs, Chapter 9.3 Page-Table Entry,
> > The size of ADDR(address) field is 12:51, but the function dma_pte_addr
> >   treats it as 12:63.
> >
> > Signed-off-by: Li, Zhen-Hua<zhen-hual@xxxxxx>
> > ---
> >   drivers/iommu/intel-iommu.c   |    4 ++--
> >   include/linux/dma_remapping.h |    2 ++
> >   2 files changed, 4 insertions(+), 2 deletions(-)
>
> Is this patching for the sake of spec interpretation?
> a dma-pte format (consumed by iommu) has 63,61:52 as available for sw, 
> ignored by hw.
> 62 is 'transient mapping' bit, which is a _hint_ for selecting iotlbs 
> to flush sooner.
> finally, the system would have to have a memory map that actually has 
> bit 62 set to
> be affected.
>
> So, for intel-iommu, I don't see a bug occurring.
> Did you actually have one with previous definition, and if so,
> could you provide that information ?
>
> Cheers,
> - Don
>
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index b4f0e28..c6d2847 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -311,10 +311,10 @@ static inline void dma_set_pte_prot(struct 
> > dma_pte *pte, unsigned long prot)
> >   static inline u64 dma_pte_addr(struct dma_pte *pte)
> >   {
> >   #ifdef CONFIG_64BIT
> > -    return pte->val&  VTD_PAGE_MASK;
> > +    return pte->val&  DMA_PTE_MASK;
> >   #else
> >       /* Must have a full atomic 64-bit read */
> > -    return  __cmpxchg64(&pte->val, 0ULL, 0ULL)& VTD_PAGE_MASK;
> > +    return  __cmpxchg64(&pte->val, 0ULL, 0ULL)& DMA_PTE_MASK;
> >   #endif
> >   }
> >
> > diff --git a/include/linux/dma_remapping.h 
> > b/include/linux/dma_remapping.h
> > index 57c9a8a..7a1e212 100644
> > --- a/include/linux/dma_remapping.h
> > +++ b/include/linux/dma_remapping.h
> > @@ -16,6 +16,8 @@
> >   #define DMA_PTE_WRITE (2)
> >   #define DMA_PTE_LARGE_PAGE (1<<  7)
> >   #define DMA_PTE_SNP (1<<  11)
> > +#define DMA_PTE_ADD_LENGTH (40)
> > +#define DMA_PTE_MASK    ((((u64)1<<  DMA_PTE_ADD_LENGTH) - 1)<<  
> > VTD_PAGE_SHIFT)
> >
> >   #define CONTEXT_TT_MULTI_LEVEL    0
> >   #define CONTEXT_TT_DEV_IOTLB    1
>
> .

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