2020-09-15 19:12:06

by Matthew Rosato

Subject: [PATCH v3] vfio iommu: Add dma available capability

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 <[email protected]>
---
drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
include/uapi/linux/vfio.h | 15 +++++++++++++++
2 files changed, 32 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..3891e03 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1039,6 +1039,21 @@ 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 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)

/**
--
1.8.3.1

2020-09-16 09:45:26

by Cornelia Huck

Subject: Re: [PATCH v3] vfio iommu: Add dma available capability

On Tue, 15 Sep 2020 15:05:18 -0400
Matthew Rosato <[email protected]> wrote:

> 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 <[email protected]>
> ---
> drivers/vfio/vfio_iommu_type1.c | 17 +++++++++++++++++
> include/uapi/linux/vfio.h | 15 +++++++++++++++
> 2 files changed, 32 insertions(+)

Reviewed-by: Cornelia Huck <[email protected]>