Re: [PATCH v16 05/16] arm64: untag user pointers passed to memory syscalls

Catalin Marinas
2019-06-11T17:44:58Z

On Tue, Jun 11, 2019 at 05:35:31PM +0200, Andrey Konovalov wrote:
> On Mon, Jun 10, 2019 at 4:28 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > On Mon, Jun 03, 2019 at 06:55:07PM +0200, Andrey Konovalov wrote:
> > > 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.
> > >
> > > This patch allows tagged pointers to be passed to the following memory
> > > syscalls: get_mempolicy, madvise, mbind, mincore, mlock, mlock2, mprotect,
> > > mremap, msync, munlock.
> > >
> > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> >
> > I would add in the commit log (and possibly in the code with a comment)
> > that mremap() and mmap() do not currently accept tagged hint addresses.
> > Architectures may interpret the hint tag as a background colour for the
> > corresponding vma. With this:
>
> I'll change the commit log. Where do you you think I should put this
> comment? Before mmap and mremap definitions in mm/?

On arm64 we use our own sys_mmap(). I'd say just add a comment on the
generic mremap() just before the untagged_addr() along the lines that
new_address is not untagged for preserving similar behaviour to mmap().

--
Catalin