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From:   "Longpeng(Mike)" <longpeng2@huawei.com>
To:     <baolu.lu@linux.intel.com>, <dwmw2@infradead.org>,
        <will@kernel.org>, <joro@8bytes.org>
CC:     <iommu@lists.linux-foundation.org>, <linux-kernel@vger.kernel.org>,
        <arei.gonglei@huawei.com>, "Longpeng(Mike)" <longpeng2@huawei.com>
Subject: [PATCH v3 2/2] iommu/vt-d: avoid duplicated removing in __domain_mapping
Date:   Fri, 8 Oct 2021 08:04:33 +0800
Message-ID: <20211008000433.1115-3-longpeng2@huawei.com>
In-Reply-To: <20211008000433.1115-1-longpeng2@huawei.com>
References: <20211008000433.1115-1-longpeng2@huawei.com>
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__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 this 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>
---
 drivers/iommu/intel/iommu.c | 11 ++++++-----
 include/linux/intel-iommu.h |  6 ++++++
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index d75f59a..46edae6 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2354,12 +2354,17 @@ static void switch_to_super_page(struct dmar_domain *domain,
 				return -ENOMEM;
 			first_pte = pte;
 
+			lvl_pages = lvl_to_nr_pages(largepage_lvl);
+
 			/* 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 +2386,6 @@ 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 9bcabc7..b29b2a3 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 IS_ALIGNED((unsigned long)pte, VTD_PAGE_SIZE);
 }
 
+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 *)ALIGN((unsigned long)pte, VTD_PAGE_SIZE) - 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);
 
-- 
1.8.3.1