Hi Andrey,

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

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.

As mentioned in the cover letter, this patchset has been merged into
the Pixel 2 kernel tree.

I just hope it's not enabled on production kernels, it would introduce
a user ABI that may differ from what ends up upstream.

-- 
Catalin

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