From 41ea432fe037b0f9c887c93bf0aaa4b1f889983c Mon Sep 17 00:00:00 2001 From: Keir Fraser Date: Fri, 16 Jul 2010 17:41:53 +0100 Subject: [PATCH] vtd: Do not update-and-flush an IOMMU PTE if it does not change. There are cases of identical repeated calls to iommu_map_page(). Flushing is slow, so it's worth detecting these and bailing early. Signed-off-by: Keir Fraser --- xen/drivers/passthrough/vtd/iommu.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c index 4cc90ac821..36c206a496 100644 --- a/xen/drivers/passthrough/vtd/iommu.c +++ b/xen/drivers/passthrough/vtd/iommu.c @@ -1591,9 +1591,8 @@ static int intel_iommu_map_page( struct hvm_iommu *hd = domain_hvm_iommu(d); struct acpi_drhd_unit *drhd; struct iommu *iommu; - struct dma_pte *page = NULL, *pte = NULL; + struct dma_pte *page = NULL, *pte = NULL, old, new = { 0 }; u64 pg_maddr; - int pte_present; int flush_dev_iotlb; int iommu_domid; @@ -1611,15 +1610,22 @@ static int intel_iommu_map_page( } page = (struct dma_pte *)map_vtd_domain_page(pg_maddr); pte = page + (gfn & LEVEL_MASK); - pte_present = dma_pte_present(*pte); - dma_set_pte_addr(*pte, (paddr_t)mfn << PAGE_SHIFT_4K); - dma_set_pte_prot(*pte, + old = *pte; + dma_set_pte_addr(new, (paddr_t)mfn << PAGE_SHIFT_4K); + dma_set_pte_prot(new, ((flags & IOMMUF_readable) ? DMA_PTE_READ : 0) | ((flags & IOMMUF_writable) ? DMA_PTE_WRITE : 0)); /* Set the SNP on leaf page table if Snoop Control available */ if ( iommu_snoop ) - dma_set_pte_snp(*pte); + dma_set_pte_snp(new); + + if ( old.val == new.val ) + { + spin_unlock(&hd->mapping_lock); + return 0; + } + *pte = new; iommu_flush_cache_entry(pte, sizeof(struct dma_pte)); spin_unlock(&hd->mapping_lock); @@ -1642,7 +1648,7 @@ static int intel_iommu_map_page( continue; if ( iommu_flush_iotlb_psi(iommu, iommu_domid, (paddr_t)gfn << PAGE_SHIFT_4K, 1, - !pte_present, flush_dev_iotlb) ) + !dma_pte_present(old), flush_dev_iotlb) ) iommu_flush_write_buffer(iommu); } -- 2.30.2