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.woodho...@intel.com>
---
drivers/iommu/intel-iommu.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index c3d4bc9..1599cb1 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)
--
1.8.5.3
--
dwmw2
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