Re: [PATCH RFC v3 2/6] riscv/mm: add untagged_addr_remote_unlocked()

[Rik van Riel]

On Mon, 2026-07-20 at 04:57 -0700, Usama Arif wrote:
> On Fri, 17 Jul 2026 13:00:32 -0400 Rik van Riel <riel@xxxxxxxxxxx>
> wrote:
> 
> 
> > 
> > mm->context.pmlen is set only through PR_SET_TAGGED_ADDR_CTRL and
> > is stable
> > afterwards, so it can be read without the mmap lock, as it already
> > is from
> > untagged_addr() and mm_untag_mask().
> > 
> 
> I think it might not be stable? set_tagged_addr_ctrl() can change it
> repeatedly until a CLONE_VM operation sets MM_CONTEXT_LOCK_PMLEN.

You're right, ARM tagged addresses seem to work a
little differently from x86 LAM.

It looks like on ARM with MTE, the top 8 bits of
the virtual address are available as tags, meaning
that address space cannot be used for VMAs.

For purposes of accessing process memory, this
is a little more stable than LAM, because the
number of bits we need to mask out of the address
is always the same when MTE is in use.

At least, I think so. Am I overlooking anything?

I will clean up the changelog like you suggested.

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