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SubjectRe: [PATCH v1 2/2] iommu/vt-d: avoid duplicated removing in __domain_mapping
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Hi Longpeng,

On 2021/9/15 23:21, Longpeng(Mike) wrote:
> __domain_mapping() always removes the pages in the range from
> 'iov_pfn' to 'end_pfn', but the 'end_pfn' is always the last pfn
> of the range that the caller wants to map.
>
> This would introduce too many duplicated removing and leads the
> map operation take too long, for example:
>
> Map iova=0x100000,nr_pages=0x7d61800
> iov_pfn: 0x100000, end_pfn: 0x7e617ff
> iov_pfn: 0x140000, end_pfn: 0x7e617ff
> iov_pfn: 0x180000, end_pfn: 0x7e617ff
> iov_pfn: 0x1c0000, end_pfn: 0x7e617ff
> iov_pfn: 0x200000, end_pfn: 0x7e617ff
> ...
> it takes about 50ms in total.
>
> We can reduce the cost by recalculate the 'end_pfn' and limit it
> to the boundary of the end of the pte page.
>
> Map iova=0x100000,nr_pages=0x7d61800
> iov_pfn: 0x100000, end_pfn: 0x13ffff
> iov_pfn: 0x140000, end_pfn: 0x17ffff
> iov_pfn: 0x180000, end_pfn: 0x1bffff
> iov_pfn: 0x1c0000, end_pfn: 0x1fffff
> iov_pfn: 0x200000, end_pfn: 0x23ffff
> ...
> it only need 9ms now.
>
> Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>

The 0day robot reports below compiling warning when building a 32-bit
kernel (make W=1 ARCH=i386):

All errors (new ones prefixed by >>):

In file included from drivers/gpu/drm/i915/i915_drv.h:43,
from
drivers/gpu/drm/i915/display/intel_display_types.h:47,
from drivers/gpu/drm/i915/display/intel_dsi.h:30,
from <command-line>:
include/linux/intel-iommu.h: In function 'nr_pte_to_next_page':
>> include/linux/intel-iommu.h:719:3: error: cast to pointer from
integer of different size [-Werror=int-to-pointer-cast]
719 | (struct dma_pte *)VTD_PAGE_ALIGN((unsigned long)pte) - pte;
| ^
cc1: all warnings being treated as errors


vim +719 include/linux/intel-iommu.h

715
716 static inline int nr_pte_to_next_page(struct dma_pte *pte)
717 {
718 return first_pte_in_page(pte) ? BIT_ULL(VTD_STRIDE_SHIFT) :
> 719 (struct dma_pte *)VTD_PAGE_ALIGN((unsigned long)pte) - pte;
720 }
721

Can you please take a look at this?

Best regards,
baolu

> ---
> drivers/iommu/intel/iommu.c | 12 +++++++-----
> include/linux/intel-iommu.h | 6 ++++++
> 2 files changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index d75f59a..87cbf34 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2354,12 +2354,18 @@ static void switch_to_super_page(struct dmar_domain *domain,
> return -ENOMEM;
> first_pte = pte;
>
> + lvl_pages = lvl_to_nr_pages(largepage_lvl);
> + BUG_ON(nr_pages < lvl_pages);
> +
> /* It is large page*/
> if (largepage_lvl > 1) {
> unsigned long end_pfn;
> + unsigned long pages_to_remove;
>
> pteval |= DMA_PTE_LARGE_PAGE;
> - end_pfn = ((iov_pfn + nr_pages) & level_mask(largepage_lvl)) - 1;
> + pages_to_remove = min_t(unsigned long, nr_pages,
> + nr_pte_to_next_page(pte) * lvl_pages);
> + end_pfn = iov_pfn + pages_to_remove - 1;
> switch_to_super_page(domain, iov_pfn, end_pfn, largepage_lvl);
> } else {
> pteval &= ~(uint64_t)DMA_PTE_LARGE_PAGE;
> @@ -2381,10 +2387,6 @@ static void switch_to_super_page(struct dmar_domain *domain,
> WARN_ON(1);
> }
>
> - lvl_pages = lvl_to_nr_pages(largepage_lvl);
> -
> - BUG_ON(nr_pages < lvl_pages);
> -
> nr_pages -= lvl_pages;
> iov_pfn += lvl_pages;
> phys_pfn += lvl_pages;
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index a590b00..4bff70c 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -713,6 +713,12 @@ static inline bool first_pte_in_page(struct dma_pte *pte)
> return !((unsigned long)pte & ~VTD_PAGE_MASK);
> }
>
> +static inline int nr_pte_to_next_page(struct dma_pte *pte)
> +{
> + return first_pte_in_page(pte) ? BIT_ULL(VTD_STRIDE_SHIFT) :
> + (struct dma_pte *)VTD_PAGE_ALIGN((unsigned long)pte) - pte;
> +}
> +
> extern struct dmar_drhd_unit * dmar_find_matched_drhd_unit(struct pci_dev *dev);
> extern int dmar_find_matched_atsr_unit(struct pci_dev *dev);
>
>

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