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

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Message-ID: <51BB7A1E.5000605@redhat.com>
Date:	Fri, 14 Jun 2013 16:16:30 -0400
From:	Don Dutile <ddutile@...hat.com>
To:	"Li, Zhen-Hua" <zhen-hual@...com>
CC:	David Woodhouse <dwmw2@...radead.org>,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/iommu: fix dma pte address size error

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@...com>
> ---
>   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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