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

[Usama Arif]

On 20/07/2026 16:08, Rik van Riel wrote:
> 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

ah do you mean RISCV here?

> 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.
>