vfio iommu: Add dma available capability

[ 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>

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 3b31e83a92155678f561f6a9571278c2cdcf384c..bc6ba41686fa3714b3e94861d02df38b5c5cb3d8 100644 (file)
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -2303,6 +2303,24 @@ out_unlock:
        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 9e843a147ead0a5812d27d876159dc1347bda51e..cabc93118f9c8faadb96c31caf292c8a57af7df3 100644 (file)
--- 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)
 
 /**