On 11/13/2019 4:00 AM, Alex Williamson wrote:
On Tue, 12 Nov 2019 22:33:38 +0530
Kirti Wankhede <kwankhede@xxxxxxxxxx> wrote:
With vIOMMU, during pre-copy phase of migration, while CPUs are still
running, IO virtual address unmap can happen while device still keeping
reference of guest pfns. Those pages should be reported as dirty before
unmap, so that VFIO user space application can copy content of those pages
from source to destination.
IOCTL defination added here add bitmap pointer, size and flag. If flag
definition, adds
VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP is set and bitmap memory is allocated
and bitmap_size of set, then ioctl will create bitmap of pinned pages and
s/of/is/
then unmap those.
Signed-off-by: Kirti Wankhede <kwankhede@xxxxxxxxxx>
Reviewed-by: Neo Jia <cjia@xxxxxxxxxx>
---
include/uapi/linux/vfio.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 6fd3822aa610..72fd297baf52 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -925,6 +925,39 @@ struct vfio_iommu_type1_dirty_bitmap {
#define VFIO_IOMMU_GET_DIRTY_BITMAP _IO(VFIO_TYPE, VFIO_BASE + 17)
+/**
+ * VFIO_IOMMU_UNMAP_DMA_GET_BITMAP - _IOWR(VFIO_TYPE, VFIO_BASE + 18,
+ * struct vfio_iommu_type1_dma_unmap_bitmap)
+ *
+ * Unmap IO virtual addresses using the provided struct
+ * vfio_iommu_type1_dma_unmap_bitmap. Caller sets argsz.
+ * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP should be set to get dirty bitmap
+ * before unmapping IO virtual addresses. If this flag is not set, only IO
+ * virtual address are unmapped without creating pinned pages bitmap, that
+ * is, behave same as VFIO_IOMMU_UNMAP_DMA ioctl.
+ * User should allocate memory to get bitmap and should set size of allocated
+ * memory in bitmap_size field. One bit in bitmap is used to represent per page
+ * consecutively starting from iova offset. Bit set indicates page at that
+ * offset from iova is dirty.
+ * The actual unmapped size is returned in the size field and bitmap of pages
+ * in the range of unmapped size is returned in bitmap if flag
+ * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP is set.
+ *
+ * No guarantee is made to the user that arbitrary unmaps of iova or size
+ * different from those used in the original mapping call will succeed.
+ */
+struct vfio_iommu_type1_dma_unmap_bitmap {
+ __u32 argsz;
+ __u32 flags;
+#define VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP (1 << 0)
+ __u64 iova; /* IO virtual address */
+ __u64 size; /* Size of mapping (bytes) */
+ __u64 bitmap_size; /* in bytes */
+ void __user *bitmap; /* one bit per page */
+};
+
+#define VFIO_IOMMU_UNMAP_DMA_GET_BITMAP _IO(VFIO_TYPE, VFIO_BASE + 18)
+
Why not extend VFIO_IOMMU_UNMAP_DMA to support this rather than add an
ioctl that duplicates the functionality and extends it??
We do want old userspace applications to work with new kernel and
vice-versa, right?
If I try to change existing VFIO_IOMMU_UNMAP_DMA ioctl structure, say if
add 'bitmap_size' and 'bitmap' after 'size', with below code in old
kernel, old kernel & new userspace will work.
minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
if (copy_from_user(&unmap, (void __user *)arg, minsz))
return -EFAULT;
if (unmap.argsz < minsz || unmap.flags)
return -EINVAL;
With new kernel it would change to:
minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, bitmap);
if (copy_from_user(&unmap, (void __user *)arg, minsz))
return -EFAULT;
if (unmap.argsz < minsz || unmap.flags)
return -EINVAL;
Then old userspace app will fail because unmap.argsz < minsz and might
be copy_from_user would cause seg fault because userspace sdk doesn't
contain new member variables.
We can't change the sequence to keep 'size' as last member, because then
new userspace app on old kernel will interpret it wrong.
Otherwise
same comments as previous, in fact it's too bad we can't use this ioctl
for both, but a DONT_UNMAP flag on the UNMAP_DMA ioctl seems a bit
absurd.
I suspect we also want a flags bit in VFIO_IOMMU_GET_INFO to indicate
these capabilities are supported.
Ok. I'll add that.
Maybe for both ioctls we also want to define it as the user's
responsibility to zero the bitmap, requiring the kernel to only set
bits as necessary.
Ok. Updating comment.
Thanks,
Kirti
Thanks,
Alex
/* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
/*
