[PATCH v3 2/2] iommu/virtio: Add ops->flush_iotlb_all and enable deferred flush

[Niklas Schnelle]

Add ops->flush_iotlb_all operation to enable virtio-iommu for the
dma-iommu deferred flush scheme. This results in a significant increase
in performance in exchange for a window in which devices can still
access previously IOMMU mapped memory when running with
CONFIG_IOMMU_DEFAULT_DMA_LAZY. The previous strict behavior can be
achieved with iommu.strict=1 on the kernel command line or
CONFIG_IOMMU_DEFAULT_DMA_STRICT.

Link: https://lore.kernel.org/lkml/20230802123612.GA6142@myrica/
Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
---
 drivers/iommu/virtio-iommu.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 3f18f69d70d8..ef6a87445105 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -926,6 +926,19 @@ static int viommu_iotlb_sync_map(struct iommu_domain *domain,
 	return viommu_sync_req(vdomain->viommu);
 }
 
+static void viommu_flush_iotlb_all(struct iommu_domain *domain)
+{
+	struct viommu_domain *vdomain = to_viommu_domain(domain);
+
+	/*
+	 * May be called before the viommu is initialized including
+	 * while creating direct mapping
+	 */
+	if (!vdomain->nr_endpoints)
+		return;
+	viommu_sync_req(vdomain->viommu);
+}
+
 static void viommu_get_resv_regions(struct device *dev, struct list_head *head)
 {
 	struct iommu_resv_region *entry, *new_entry, *msi = NULL;
@@ -1051,6 +1064,8 @@ static bool viommu_capable(struct device *dev, enum iommu_cap cap)
 	switch (cap) {
 	case IOMMU_CAP_CACHE_COHERENCY:
 		return true;
+	case IOMMU_CAP_DEFERRED_FLUSH:
+		return true;
 	default:
 		return false;
 	}
@@ -1071,6 +1086,7 @@ static struct iommu_ops viommu_ops = {
 		.map_pages		= viommu_map_pages,
 		.unmap_pages		= viommu_unmap_pages,
 		.iova_to_phys		= viommu_iova_to_phys,
+		.flush_iotlb_all	= viommu_flush_iotlb_all,
 		.iotlb_sync		= viommu_iotlb_sync,
 		.iotlb_sync_map		= viommu_iotlb_sync_map,
 		.free			= viommu_domain_free,

-- 
2.39.2