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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>
This commit is contained in:
David Woodhouse 2014-03-11 17:10:29 -07:00 committed by David Woodhouse
parent 214e39aa36
commit d050196087
1 changed files with 17 additions and 4 deletions
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21
drivers/iommu/intel-iommu.c
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@ -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;
struct dmar_drhd_unit *drhd;
struct intel_iommu *iommu;
int i, found = 0;
i = find_first_bit(domain->iommu_bmp, g_num_of_iommus);
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)