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Subject[PATCH 5.4 02/62] vfio iommu: Add dma available capability
Date
From: Matthew Rosato <mjrosato@linux.ibm.com>

[ Upstream commit 7d6e1329652ed971d1b6e0e7bea66fba5044e271 ]

The following functional changes were needed for backport:
- vfio_iommu_type1_get_info doesn't exist, call
vfio_iommu_dma_avail_build_caps from vfio_iommu_type1_ioctl.
- As further fallout from this, vfio_iommu_dma_avail_build_caps must
acquire and release the iommu mutex lock. To do so, the return value is
stored in a local variable as in vfio_iommu_iova_build_caps.

Upstream commit description:
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/vfio/vfio_iommu_type1.c | 22 ++++++++++++++++++++++
include/uapi/linux/vfio.h | 15 +++++++++++++++
2 files changed, 37 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 3b31e83a92155..bc6ba41686fa3 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2303,6 +2303,24 @@ static int vfio_iommu_iova_build_caps(struct vfio_iommu *iommu,
return ret;
}

+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;
+ int ret;
+
+ mutex_lock(&iommu->lock);
+ cap_dma_avail.header.id = VFIO_IOMMU_TYPE1_INFO_DMA_AVAIL;
+ cap_dma_avail.header.version = 1;
+
+ cap_dma_avail.avail = iommu->dma_avail;
+
+ ret = vfio_info_add_capability(caps, &cap_dma_avail.header,
+ sizeof(cap_dma_avail));
+ mutex_unlock(&iommu->lock);
+ return ret;
+}
+
static long vfio_iommu_type1_ioctl(void *iommu_data,
unsigned int cmd, unsigned long arg)
{
@@ -2349,6 +2367,10 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
info.iova_pgsizes = vfio_pgsize_bitmap(iommu);

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

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 9e843a147ead0..cabc93118f9c8 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -748,6 +748,21 @@ struct vfio_iommu_type1_info_cap_iova_range {
struct vfio_iova_range iova_ranges[];
};

+/*
+ * The DMA available capability allows to report the current number of
+ * simultaneously outstanding DMA mappings that are allowed.
+ *
+ * The structure below defines version 1 of this capability.
+ *
+ * avail: specifies the current 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)

/**
--
2.27.0


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