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Subject[PATCH] vfio/type1: Search for a fitting iommu_domain before attaching the iommu_group
Date
... 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 <sironi@amazon.de>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: kvm@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
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