[PATCH] vfio/type1: Search for a fitting iommu_domain before attaching the iommu_group

[Filippo Sironi]

... to avoid an unnecessary attach/detach of the iommu_group to the
newly created iommu_domain.  This also saves us a context-cache and an
IOTLB flush.

This is possible because allocating an iommu_domain for the iommu_group
we're attaching is enough to understand whether a fitting iommu_domain
already exists.

Signed-off-by: Filippo Sironi <sir...@amazon.de>
Cc: Alex Williamson <alex.william...@redhat.com>
Cc: k...@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/vfio/vfio_iommu_type1.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 45657e2b1ff7..88359b4993f3 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -1279,15 +1279,8 @@ static int vfio_iommu_type1_attach_group(void 
*iommu_data,
                        goto out_domain;
        }
 
-       ret = iommu_attach_group(domain->domain, iommu_group);
-       if (ret)
-               goto out_domain;
-
        resv_msi = vfio_iommu_has_sw_msi(iommu_group, &resv_msi_base);
 
-       INIT_LIST_HEAD(&domain->group_list);
-       list_add(&group->next, &domain->group_list);
-
        msi_remap = irq_domain_check_msi_remap() ||
                    iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
 
@@ -1295,7 +1288,7 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
                pr_warn("%s: No interrupt remapping support.  Use the module 
param \"allow_unsafe_interrupts\" to enable VFIO IOMMU support on this 
platform\n",
                       __func__);
                ret = -EPERM;
-               goto out_detach;
+               goto out_domain;
        }
 
        if (iommu_capable(bus, IOMMU_CAP_CACHE_COHERENCY))
@@ -1311,21 +1304,24 @@ static int vfio_iommu_type1_attach_group(void 
*iommu_data,
        list_for_each_entry(d, &iommu->domain_list, next) {
                if (d->domain->ops == domain->domain->ops &&
                    d->prot == domain->prot) {
-                       iommu_detach_group(domain->domain, iommu_group);
-                       if (!iommu_attach_group(d->domain, iommu_group)) {
-                               list_add(&group->next, &d->group_list);
-                               iommu_domain_free(domain->domain);
-                               kfree(domain);
-                               mutex_unlock(&iommu->lock);
-                               return 0;
-                       }
-
-                       ret = iommu_attach_group(domain->domain, iommu_group);
+                       ret = iommu_attach_group(d->domain, iommu_group);
                        if (ret)
                                goto out_domain;
+                       list_add(&group->next, &d->group_list);
+                       iommu_domain_free(domain->domain);
+                       kfree(domain);
+                       mutex_unlock(&iommu->lock);
+                       return 0;
                }
        }
 
+       ret = iommu_attach_group(domain->domain, iommu_group);
+       if (ret)
+               goto out_domain;
+
+       INIT_LIST_HEAD(&domain->group_list);
+       list_add(&group->next, &domain->group_list);
+
        vfio_test_domain_fgsp(domain);
 
        /* replay mappings on new domains */
-- 
2.7.4