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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2025 08:54:36.4482 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d0a2bb6d-2971-43ee-7d74-08dd8c7ba0f2 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: DU6PEPF0000B620.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB10027 Hi Ryan, > 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. > > 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. > Personally, I don't believe this because the create_init_idmap() maps the the .rodata section with PAGE_KERNEL pgprot from __initdata_begin to _end. and at the mark_readonly() the pgprot is changed to PAGE_KERNEL_RO But, arm64_use_ng_mappings is accessed with write before mark_readonly() only via smp_cpus_done(). JFYI here is map information: // mark_readlonly() changes to ro perm below ranges: ffff800081b30000 g .rodata 0000000000000000 __start_rodata ffff800082560000 g .rodata.text 0000000000000000 __init_begin // create_init_idmap() maps below range with PAGE_KERNEL. ffff8000826d0000 g .altinstructions 0000000000000000 __initdata_begin ffff800082eb0000 g .bss 0000000000000000 _end ffff8000824596d0 g O .rodata 0000000000000001 arm64_use_ng_mappings Thanks. > Thanks, > Ryan > > > > > Thanks to let me know. But still I've failed to reproduce this > > on Cortex-a72 and any older cpu on qeum. > > If you don't mind, would you share your Kconfig? > > > >> I haven't debugged it yet but I wonder whether something wants to write > >> this variable after it was made read-only (well, I couldn't find any by > >> grep'ing the code, so it needs some step-by-step debugging). > >> > > [...] > > > > Thanks! > > > > -- > > Sincerely, > > Yeoreum Yun > -- Sincerely, Yeoreum Yun