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Subject[PATCH v2] vfio iommu: Add dma available capability
Date
Commit 492855939bdb ("vfio/type1: Limit DMA mappings per container")
added the ability to limit the number of memory backed DMA mappings.
However on s390x, when lazy mapping is in use, we use a very large
number of concurrent mappings. Let's provide the current allowable
number of DMA mappings to userspace via the IOMMU info chain so that
userspace can take appropriate mitigation.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
include/uapi/linux/vfio.h | 16 ++++++++++++++++
2 files changed, 33 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 5fbf0c1..15e21db 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2609,6 +2609,20 @@ static int vfio_iommu_migration_build_caps(struct vfio_iommu *iommu,
return vfio_info_add_capability(caps, &cap_mig.header, sizeof(cap_mig));
}

+static int vfio_iommu_dma_avail_build_caps(struct vfio_iommu *iommu,
+ struct vfio_info_cap *caps)
+{
+ struct vfio_iommu_type1_info_dma_avail cap_dma_avail;
+
+ cap_dma_avail.header.id = VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL;
+ cap_dma_avail.header.version = 1;
+
+ cap_dma_avail.avail = iommu->dma_avail;
+
+ return vfio_info_add_capability(caps, &cap_dma_avail.header,
+ sizeof(cap_dma_avail));
+}
+
static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu,
unsigned long arg)
{
@@ -2642,6 +2656,9 @@ static int vfio_iommu_type1_get_info(struct vfio_iommu *iommu,
ret = vfio_iommu_migration_build_caps(iommu, &caps);

if (!ret)
+ ret = vfio_iommu_dma_avail_build_caps(iommu, &caps);
+
+ if (!ret)
ret = vfio_iommu_iova_build_caps(iommu, &caps);

mutex_unlock(&iommu->lock);
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 9204705..a8cc4a5 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1039,6 +1039,22 @@ struct vfio_iommu_type1_info_cap_migration {
__u64 max_dirty_bitmap_size; /* in bytes */
};

+/*
+ * The DMA available capability allows to report the current number of
+ * simultaneously outstanding DMA mappings that are allowed.
+ *
+ * The structures below define version 1 of this capability.
+ *
+ * max: specifies the maximum number of outstanding DMA mappings allowed.
+ */
+#define VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL 3
+
+struct vfio_iommu_type1_info_dma_avail {
+ struct vfio_info_cap_header header;
+ __u32 avail;
+};
+
+
#define VFIO_IOMMU_GET_INFO _IO(VFIO_TYPE, VFIO_BASE + 12)

/**
--
1.8.3.1
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