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 <[email protected]> --- In fact, even the overly cautious approach is broken because it's possible to add a coherent IOMMU, then set up some mappings and *then* add a non- coherent IOMMU. What we really want to do is flush the dcache at the time a domain transitions from coherent to non-coherent. Except that would unfortunately involve doing wbinvd on *all* CPUs, and something vaguely equivalent on IA64 that I'm not sure even exists. Walking the page tables and manually doing a clflush_cache_range() on them all would also be theoretically possible but I'm fairly sure we don't want to do that... 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 86bfc4b..0b16592 100644 --- a/drivers/iommu/intel-iommu.c +++ b/drivers/iommu/intel-iommu.c @@ -593,18 +593,31 @@ 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 -- David Woodhouse Open Source Technology Centre [email protected] Intel Corporation
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