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Mon, 2 Feb 2026 03:11:46 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ThreadId: ASnEhGskTYsw Date: Mon, 02 Feb 2026 09:11:26 +0100 From: "Arnd Bergmann" To: "Ard Biesheuvel" , "Yang Shi" , "Catalin Marinas" , "Will Deacon" , "Ryan Roberts" , "Andrew Morton" , "David Hildenbrand" , "Lorenzo Stoakes" , "Dev Jain" , scott@os.amperecomputing.com, "Christoph Lameter (Ampere)" Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Message-Id: <625eaac4-6972-4d4e-ac8d-52cc19e4fe33@app.fastmail.com> In-Reply-To: References: <20250917190323.3828347-1-yang@os.amperecomputing.com> <20250917190323.3828347-5-yang@os.amperecomputing.com> Subject: Re: [PATCH v8 4/5] arm64: mm: split linear mapping if BBML2 unsupported on secondary CPUs Content-Type: text/plain Content-Transfer-Encoding: 7bit On Mon, Feb 2, 2026, at 08:43, Ard Biesheuvel wrote: > On Mon, 2 Feb 2026, at 08:18, Arnd Bergmann wrote: >> On Wed, Sep 17, 2025, at 21:02, Yang Shi wrote: >> --- a/arch/arm64/mm/proc.S >> +++ b/arch/arm64/mm/proc.S >> @@ -439,7 +439,7 @@ SYM_FUNC_END(idmap_kpti_install_ng_mappings) >> #endif >> >> .pushsection ".idmap.text", "a" >> -SYM_TYPED_FUNC_START(wait_linear_map_split_to_ptes) >> +SYM_FUNC_START(wait_linear_map_split_to_ptes) >> /* Must be same registers as in idmap_kpti_install_ng_mappings */ >> swapper_ttb .req x3 >> flag_ptr .req x4 >> > > This is not the right fix: the indirect call from > linear_map_split_to_ptes() will be instrumented, and so it requires the > CFI annotation to precede the function entry point, which is what > SYM_TYPED_FUNC_START() is supposed to emit. > > The typeid symbol is injected by the compiler into every object file > that takes the address of the function in question, and so the fact > that it is missing seems to suggest that linear_map_split_to_ptes() has > been optimized away entirely. Could you double check > arch/arm64/mm/mmu.o if that is the case? Ah, thanks for the explanation. This has indeed been optimized out by a patch in my randconfig tree that makes CONFIG_SMP optional for arm64. Without SMP, the calling code path is never used because smp_processor_id() is fixed to 0. I'll fix up that other patch then. Arnd