On Thu, Dec 06, 2018 at 01:44:24PM +0100, Andrey Konovalov wrote:

On Thu, Nov 29, 2018 at 7:16 PM Catalin Marinas [off-list ref] wrote:

quoted

On Thu, Nov 08, 2018 at 03:48:10PM +0100, Andrey Konovalov wrote:

quoted

On Thu, Nov 8, 2018 at 3:36 PM, Andrey Konovalov [off-list ref] wrote:

quoted

Changes in v8:
- Rebased onto 65102238 (4.20-rc1).
- Added a note to the cover letter on why syscall wrappers/shims that untag
  user pointers won't work.
- Added a note to the cover letter that this patchset has been merged into
  the Pixel 2 kernel tree.
- Documentation fixes, in particular added a list of syscalls that don't
  support tagged user pointers.

I've changed the documentation to be more specific, please take a look.

I haven't done anything about adding a way for the user to find out
that the kernel supports this ABI extension. I don't know what would
the the preferred way to do this, and we haven't received any comments
on that from anybody else. Probing "on some innocuous syscall
currently returning -EFAULT on tagged pointer arguments" works though,
as you mentioned.

We've had some internal discussions and also talked to some people at
Plumbers. I think the best option is to introduce an AT_FLAGS bit to
describe the ABI relaxation on tagged pointers. Vincenzo is going to
propose a patch on top of this series.

So should I wait for a patch from Vincenzo before posting v9 or post
it as is? Or try to develop this patch myself?

The reason Vincenzo hasn't posted his patches yet is that we are still
debating internally how to document which syscalls accept non-zero
top-byte, what to do with future syscalls for which we don't know the
semantics.

Happy to take the discussion to the public list if Vincenzo posts his
patches. The conclusion of the ABI discussion may have an impact on the
actual implementation that you are proposing in this series.

-- 
Catalin