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[1/6] iommu/dma: Stop getting dma_32bit_pfn wrong

Message ID 20170503203234.32313-1-manoj.iyer@canonical.com
State New
Headers show

Commit Message

Manoj Iyer May 3, 2017, 8:32 p.m. UTC 
From: Robin Murphy <robin.murphy@arm.com>

iommu_dma_init_domain() was originally written under the misconception
that dma_32bit_pfn represented some sort of size limit for IOVA domains.
Since the truth is almost the exact opposite of that, rework the logic
and comments to reflect its real purpose of optimising lookups when
allocating from a subset of the available 64-bit space.

BugLink: http://bugs.launchpad.net/bugs/1680549

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
(cherry picked from commit f51d7bb79c1124f7f02e9f472ef935eba13bca8e)
Signed-off-by: Manoj Iyer <manoj.iyer@canonical.com>
---
 drivers/iommu/dma-iommu.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)
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Patch

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index de41ead6542a..9aa432e8fbd3 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -203,6 +203,7 @@  int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 	struct iommu_dma_cookie *cookie = domain->iova_cookie;
 	struct iova_domain *iovad = &cookie->iovad;
 	unsigned long order, base_pfn, end_pfn;
+	bool pci = dev && dev_is_pci(dev);
 
 	if (!cookie || cookie->type != IOMMU_DMA_IOVA_COOKIE)
 		return -EINVAL;
@@ -225,19 +226,31 @@  int iommu_dma_init_domain(struct iommu_domain *domain, dma_addr_t base,
 		end_pfn = min_t(unsigned long, end_pfn,
 				domain->geometry.aperture_end >> order);
 	}
+	/*
+	 * PCI devices may have larger DMA masks, but still prefer allocating
+	 * within a 32-bit mask to avoid DAC addressing. Such limitations don't
+	 * apply to the typical platform device, so for those we may as well
+	 * leave the cache limit at the top of their range to save an rb_last()
+	 * traversal on every allocation.
+	 */
+	if (pci)
+		end_pfn &= DMA_BIT_MASK(32) >> order;
 
-	/* All we can safely do with an existing domain is enlarge it */
+	/* start_pfn is always nonzero for an already-initialised domain */
 	if (iovad->start_pfn) {
 		if (1UL << order != iovad->granule ||
-		    base_pfn != iovad->start_pfn ||
-		    end_pfn < iovad->dma_32bit_pfn) {
+		    base_pfn != iovad->start_pfn) {
 			pr_warn("Incompatible range for DMA domain\n");
 			return -EFAULT;
 		}
-		iovad->dma_32bit_pfn = end_pfn;
+		/*
+		 * If we have devices with different DMA masks, move the free
+		 * area cache limit down for the benefit of the smaller one.
+		 */
+		iovad->dma_32bit_pfn = min(end_pfn, iovad->dma_32bit_pfn);
 	} else {
 		init_iova_domain(iovad, 1UL << order, base_pfn, end_pfn);
-		if (dev && dev_is_pci(dev))
+		if (pci)
 			iova_reserve_pci_windows(to_pci_dev(dev), iovad);
 	}
 	return 0;