[PATCH 9/9] iommu/vt-d: Avoid duplicate removing in __domain_mapping()

Lu Baolu
2021-10-14T05:43:06Z

From: "Longpeng(Mike)" <longpeng2@huawei.com>

The __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.

This also removes a meaningless BUG_ON() in __domain_mapping().

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
Tested-by: Liujunjie <liujunjie23@huawei.com>
Link: https://lore.kernel.org/r/20211008000433.1115-1-longpeng2@huawei.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
include/linux/intel-iommu.h | 6 ++++++
drivers/iommu/intel/iommu.c | 11 ++++++-----
2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 52481625838c..69230fd695ea 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -710,6 +710,12 @@ 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);

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 16a35669a9d0..0bde0c8b4126 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2479,12 +2479,17 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
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;
@@ -2506,10 +2511,6 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
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;