Re: [PATCH v16 12/16] IB, arm64: untag user pointers in ib_uverbs_(re)reg_mr()

On Tue, Jun 4, 2019 at 2:27 PM Jason Gunthorpe [off-list ref] wrote:

On Tue, Jun 04, 2019 at 02:18:19PM +0200, Andrey Konovalov wrote:

quoted

On Mon, Jun 3, 2019 at 7:46 PM Jason Gunthorpe [off-list ref] wrote:

quoted

On Mon, Jun 03, 2019 at 06:55:14PM +0200, Andrey Konovalov wrote:

quoted

This patch is a part of a series that extends arm64 kernel ABI to allow to
pass tagged user pointers (with the top byte set to something else other
than 0x00) as syscall arguments.

ib_uverbs_(re)reg_mr() use provided user pointers for vma lookups (through
e.g. mlx4_get_umem_mr()), which can only by done with untagged pointers.

Untag user pointers in these functions.

Signed-off-by: Andrey Konovalov <redacted>
 drivers/infiniband/core/uverbs_cmd.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
index 5a3a1780ceea..f88ee733e617 100644
+++ b/drivers/infiniband/core/uverbs_cmd.c

@@ -709,6 +709,8 @@ static int ib_uverbs_reg_mr(struct uverbs_attr_bundle *attrs)
      if (ret)
              return ret;

+     cmd.start = untagged_addr(cmd.start);
+
      if ((cmd.start & ~PAGE_MASK) != (cmd.hca_va & ~PAGE_MASK))
              return -EINVAL;

I feel like we shouldn't thave to do this here, surely the cmd.start
should flow unmodified to get_user_pages, and gup should untag it?

ie, this sort of direction for the IB code (this would be a giant
patch, so I didn't have time to write it all, but I think it is much
saner):

Hi Jason,

ib_uverbs_reg_mr() passes cmd.start to mlx4_get_umem_mr(), which calls
find_vma(), which only accepts untagged addresses. Could you explain
how your patch helps?

That mlx4 is just a 'weird duck', it is not the normal flow, and I
don't think the core code should be making special consideration for
it.

How do you think we should do untagging (or something else) to deal
with this 'weird duck' case?

Jason

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