iommu/vt-d: Be less pessimistic about domain coherency where possible (d0501960) · Commits · 戴 / test

In commit ("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>

drivers/iommu/intel-iommu.c

+17 −4

Original line number	Diff line number	Diff line
		@@ -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)

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