linux-kernel - [Question] mprotect() can't clear PROT

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Message-ID: <04ea9978-e6aa-4498-b899-76d56e19b084@os.amperecomputing.com>
Date: Wed, 29 Oct 2025 15:41:17 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: LAK <linux-arm-kernel@...ts.infradead.org>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [Question] mprotect() can't clear PROT_MTE

Hi Catalin,

Our customers have usecase to untag memory w/o unmapping it, but 
mprotect can't do it. It seems like an intended behavior because I saw 
MTE doc explicitly says PROT_MTE flags can't be cleared by mprotect().
But I don't see why mprotect() can't do it if I don't miss anything. So 
I'd like to know why it behaves in this way.

unmap + mmap or mmap(MAP_FIXED) can do the trick, but it is not feasible 
for anonymous mapping because unamp will wipe all the data.

Thanks,
Yang