# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1279298513 -3600
# Node ID 07b718833c7416b06a3aee61a0bf27c2e1df1160
# Parent e382656e4dccab583006352ca131af9da623673a
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 <keir.fraser@xxxxxxxxxx>
---
xen/drivers/passthrough/vtd/iommu.c | 20 +++++++++++++-------
1 files changed, 13 insertions(+), 7 deletions(-)
diff -r e382656e4dcc -r 07b718833c74 xen/drivers/passthrough/vtd/iommu.c
--- a/xen/drivers/passthrough/vtd/iommu.c Fri Jul 16 16:19:51 2010 +0100
+++ b/xen/drivers/passthrough/vtd/iommu.c Fri Jul 16 17:41:53 2010 +0100
@@ -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);
}
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