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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2025 10:48:26.2810 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a0eecdb4-87e9-40a3-609f-08dd8c8b87d6 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DU2PEPF00028D0A.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB6149 > On 06/05/2025 10:41, Ard Biesheuvel wrote: > > On Tue, 6 May 2025 at 10:16, Ryan Roberts wrote: > >> > >> On 06/05/2025 09:09, Yeoreum Yun wrote: > >>> Hi Catalin, > >>> > >>>> On Sat, May 03, 2025 at 09:23:27PM +0100, Yeoreum Yun wrote: > >>>>> Hi Catalin, > >>>>> > >>>>>> On Sat, May 03, 2025 at 11:16:12AM +0100, Catalin Marinas wrote: > >>>>>>> On Fri, 02 May 2025 19:04:12 +0100, Yeoreum Yun wrote: > >>>>>>>> create_init_idmap() could be called before .bss section initialization > >>>>>>>> which is done in early_map_kernel(). > >>>>>>>> Therefore, data/test_prot could be set incorrectly by PTE_MAYBE_NG macro. > >>>>>>>> > >>>>>>>> PTE_MAYBE_NG macro set NG bit according to value of "arm64_use_ng_mappings". > >>>>>>>> and this variable places in .bss section. > >>>>>>>> > >>>>>>>> [...] > >>>>>>> > >>>>>>> Applied to arm64 (for-next/fixes), with some slight tweaking of the > >>>>>>> comment, thanks! > >>>>>>> > >>>>>>> [1/1] arm64/cpufeature: annotate arm64_use_ng_mappings with ro_after_init to prevent wrong idmap generation > >>>>>>> https://git.kernel.org/arm64/c/12657bcd1835 > >>>>>> > >>>>>> I'm going to drop this for now. The kernel compiled with a clang 19.1.5 > >>>>>> version I have around (Debian sid) fails to boot, gets stuck early on: > >>>>>> > >>>>>> $ clang --version > >>>>>> Debian clang version 19.1.5 (1) > >>>>>> Target: aarch64-unknown-linux-gnu > >>>>>> Thread model: posix > >>>>>> InstalledDir: /usr/lib/llvm-19/bin > >>>>>> > >>>>>> I didn't have time to investigate, disassemble etc. I'll have a look > >>>>>> next week. > >>>>> > >>>>> Just for your information. > >>>>> When I see the debian package, clang 19.1.5-1 doesn't supply anymore: > >>>>> - https://ftp.debian.org/debian/pool/main/l/llvm-toolchain-19/ > >>>>> > >>>>> and the default version for sid is below: > >>>>> > >>>>> $ clang-19 --version > >>>>> Debian clang version 19.1.7 (3) > >>>>> Target: aarch64-unknown-linux-gnu > >>>>> Thread model: posix > >>>>> InstalledDir: /usr/lib/llvm-19/bin > >>>>> > >>>>> When I tested with above version with arm64-linux's for-next/fixes > >>>>> including this patch. it works well. > >>>> > >>>> It doesn't seem to be toolchain related. It fails with gcc as well from > >>>> Debian stable but you'd need some older CPU (even if emulated, e.g. > >>>> qemu). It fails with Cortex-A72 (guest on Raspberry Pi 4) but not > >>>> Neoverse-N2. Also changing the annotation from __ro_after_init to > >>>> __read_mostly also works. > >> > >> I think this is likely because __ro_after_init is also "ro before init" - i.e. > >> if you try to write to it in the PI code an exception is generated due to it > >> being mapped RO. Looks like early_map_kernel() is writiing to it. > >> > > > > Indeed. > > > >> I've noticed a similar problem in the past and it would be nice to fix it so > >> that PI code maps __ro_after_init RW. > >> > > > > The issue is that the store occurs via the ID map, which only consists > > of one R-X and one RW- section. I'm not convinced that it's worth the > > hassle to relax this. > > > > If moving the variable to .data works, then let's just do that. > > Yeah, fair enough. Thanks. I've success to reproduce. and after check, Sending with this fix. -- Sincerely, Yeoreum Yun