Re: [PATCH] iommu/vt-d: Fix a bug in intel_iommu_iova_to_phys() for huge page

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Yonghyun,

Thanks for the patch.

On 2020/2/19 6:23, Yonghyun Hwang wrote:
> intel_iommu_iova_to_phys() has a bug when it translates an IOVA for a huge
> page onto its corresponding physical address. This commit fixes the bug by
> accomodating the level of page entry for the IOVA and adds IOVA's lower
> address to the physical address. >
> Signed-off-by: Yonghyun Hwang <yonghyun@google.com>
> ---
>   drivers/iommu/intel-iommu.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 0c8d81f56a30..ed6e69adb578 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5555,13 +5555,20 @@ static phys_addr_t intel_iommu_iova_to_phys(struct iommu_domain *domain,
>   	struct dma_pte *pte;
>   	int level = 0;
>   	u64 phys = 0;
> +	const unsigned long pfn = iova >> VTD_PAGE_SHIFT;

Why do you need a "const unsigned long" here?

>   
>   	if (dmar_domain->flags & DOMAIN_FLAG_LOSE_CHILDREN)
>   		return 0;
>   
> -	pte = pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT, &level);
> -	if (pte)
> +	pte = pfn_to_dma_pte(dmar_domain, pfn, &level);
> +	if (pte) {
>   		phys = dma_pte_addr(pte);
> +		if (level > 1)
> +			phys += (pfn &
> +				((1UL << level_to_offset_bits(level)) - 1))
> +				<< VTD_PAGE_SHIFT;
> +		phys += iova & (VTD_PAGE_SIZE - 1);

How about

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 9dc37672bf89..bd17c2510bb2 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -5693,8 +5693,14 @@ static phys_addr_t 
intel_iommu_iova_to_phys(struct iommu_domain *domain,
         u64 phys = 0;

         pte = pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT, &level);
-       if (pte)
+       if (pte) {
+               unsigned long offset_mask;
+
+               offset_mask = BIT_MASK(level_to_offset_bits(level) +
+                                      VTD_PAGE_SHIFT) - 1;
                 phys = dma_pte_addr(pte);
+               phys += iova & (bitmask - 1);
+       }

         return phys;
  }

Best regards,
baolu