From: David Woodhouse <dwmw2@infradead.org>
Date: Wed, 12 Mar 2014 00:10:29 +0000 (-0700)
Subject: iommu/vt-d: Be less pessimistic about domain coherency where possible
X-Git-Tag: v3.15-rc1~70^2^6~37
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=d05019608746240d86a406fbf8d8c1fc71a87101;p=karo-tx-linux.git

iommu/vt-d: Be less pessimistic about domain coherency where possible

In commit 2e12bc29 ("intel-iommu: Default to non-coherent for domains
unattached to iommus") we decided to err on the side of caution and
always assume that it's possible that a device will be attached which is
behind a non-coherent IOMMU.

In some cases, however, that just *cannot* happen. If there *are* no
IOMMUs in the system which are non-coherent, then we don't need to do
it. And flushing the dcache is a *significant* performance hit.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
---

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index c3d4bc91a189..1599cb1e041c 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -592,18 +592,31 @@ static struct intel_iommu *domain_get_iommu(struct dmar_domain *domain)
 
 static void domain_update_iommu_coherency(struct dmar_domain *domain)
 {
-	int i;
-
-	i = find_first_bit(domain->iommu_bmp, g_num_of_iommus);
+	struct dmar_drhd_unit *drhd;
+	struct intel_iommu *iommu;
+	int i, found = 0;
 
-	domain->iommu_coherency = i < g_num_of_iommus ? 1 : 0;
+	domain->iommu_coherency = 1;
 
 	for_each_set_bit(i, domain->iommu_bmp, g_num_of_iommus) {
+		found = 1;
 		if (!ecap_coherent(g_iommus[i]->ecap)) {
 			domain->iommu_coherency = 0;
 			break;
 		}
 	}
+	if (found)
+		return;
+
+	/* No hardware attached; use lowest common denominator */
+	rcu_read_lock();
+	for_each_active_iommu(iommu, drhd) {
+		if (!ecap_coherent(iommu->ecap)) {
+			domain->iommu_coherency = 0;
+			break;
+		}
+	}
+	rcu_read_unlock();
 }
 
 static void domain_update_iommu_snooping(struct dmar_domain *domain)