arm64: dts: qcom: qcm6490-shift-otter: reduce rmtfs_mem from 6MiB to 2.5MiB#12
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arm64: dts: qcom: qcm6490-shift-otter: reduce rmtfs_mem from 6MiB to 2.5MiB#12MatthewCroughan wants to merge 1 commit into
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…2.5MiB The downstream dts still has this at 2.5MiB unlike counterparts such as the Fairphone 5 who set it to 6MiB
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Worth noting that I haven't tested the changes don't break something like the modem yet. |
MatthewCroughan
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This may change with the A16 BSP updates, which also bump the downstream kernel to 6.12. |
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@amartinz So you say we wait until at least A16 is known what it needs? I don't know yet either from Fairphone side. |
I would prefer to wait, yes. 3.5 MB more or less is neglectable for a device with 12 GB of RAM in this stage of development, if you ask me 😄 |
z3ntu
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Jan 23, 2026
commit 0031241 upstream. On systems using the hash MMU, there is a software SLB preload cache that mirrors the entries loaded into the hardware SLB buffer. This preload cache is subject to periodic eviction — typically after every 256 context switches — to remove old entry. To optimize performance, the kernel skips switch_mmu_context() in switch_mm_irqs_off() when the prev and next mm_struct are the same. However, on hash MMU systems, this can lead to inconsistencies between the hardware SLB and the software preload cache. If an SLB entry for a process is evicted from the software cache on one CPU, and the same process later runs on another CPU without executing switch_mmu_context(), the hardware SLB may retain stale entries. If the kernel then attempts to reload that entry, it can trigger an SLB multi-hit error. The following timeline shows how stale SLB entries are created and can cause a multi-hit error when a process moves between CPUs without a MMU context switch. CPU 0 CPU 1 ----- ----- Process P exec swapper/1 load_elf_binary begin_new_exc activate_mm switch_mm_irqs_off switch_mmu_context switch_slb /* * This invalidates all * the entries in the HW * and setup the new HW * SLB entries as per the * preload cache. */ context_switch sched_migrate_task migrates process P to cpu-1 Process swapper/0 context switch (to process P) (uses mm_struct of Process P) switch_mm_irqs_off() switch_slb load_slb++ /* * load_slb becomes 0 here * and we evict an entry from * the preload cache with * preload_age(). We still * keep HW SLB and preload * cache in sync, that is * because all HW SLB entries * anyways gets evicted in * switch_slb during SLBIA. * We then only add those * entries back in HW SLB, * which are currently * present in preload_cache * (after eviction). */ load_elf_binary continues... setup_new_exec() slb_setup_new_exec() sched_switch event sched_migrate_task migrates process P to cpu-0 context_switch from swapper/0 to Process P switch_mm_irqs_off() /* * Since both prev and next mm struct are same we don't call * switch_mmu_context(). This will cause the HW SLB and SW preload * cache to go out of sync in preload_new_slb_context. Because there * was an SLB entry which was evicted from both HW and preload cache * on cpu-1. Now later in preload_new_slb_context(), when we will try * to add the same preload entry again, we will add this to the SW * preload cache and then will add it to the HW SLB. Since on cpu-0 * this entry was never invalidated, hence adding this entry to the HW * SLB will cause a SLB multi-hit error. */ load_elf_binary continues... START_THREAD start_thread preload_new_slb_context /* * This tries to add a new EA to preload cache which was earlier * evicted from both cpu-1 HW SLB and preload cache. This caused the * HW SLB of cpu-0 to go out of sync with the SW preload cache. The * reason for this was, that when we context switched back on CPU-0, * we should have ideally called switch_mmu_context() which will * bring the HW SLB entries on CPU-0 in sync with SW preload cache * entries by setting up the mmu context properly. But we didn't do * that since the prev mm_struct running on cpu-0 was same as the * next mm_struct (which is true for swapper / kernel threads). So * now when we try to add this new entry into the HW SLB of cpu-0, * we hit a SLB multi-hit error. */ WARNING: CPU: 0 PID: 1810970 at arch/powerpc/mm/book3s64/slb.c:62 assert_slb_presence+0x2c/0x50(48 results) 02:47:29 [20157/42149] Modules linked in: CPU: 0 UID: 0 PID: 1810970 Comm: dd Not tainted 6.16.0-rc3-dirty #12 VOLUNTARY Hardware name: IBM pSeries (emulated by qemu) POWER8 (architected) 0x4d0200 0xf000004 of:SLOF,HEAD hv:linux,kvm pSeries NIP: c00000000015426c LR: c0000000001543b4 CTR: 0000000000000000 REGS: c0000000497c77e0 TRAP: 0700 Not tainted (6.16.0-rc3-dirty) MSR: 8000000002823033 <SF,VEC,VSX,FP,ME,IR,DR,RI,LE> CR: 28888482 XER: 00000000 CFAR: c0000000001543b0 IRQMASK: 3 <...> NIP [c00000000015426c] assert_slb_presence+0x2c/0x50 LR [c0000000001543b4] slb_insert_entry+0x124/0x390 Call Trace: 0x7fffceb5ffff (unreliable) preload_new_slb_context+0x100/0x1a0 start_thread+0x26c/0x420 load_elf_binary+0x1b04/0x1c40 bprm_execve+0x358/0x680 do_execveat_common+0x1f8/0x240 sys_execve+0x58/0x70 system_call_exception+0x114/0x300 system_call_common+0x160/0x2c4 >From the above analysis, during early exec the hardware SLB is cleared, and entries from the software preload cache are reloaded into hardware by switch_slb. However, preload_new_slb_context and slb_setup_new_exec also attempt to load some of the same entries, which can trigger a multi-hit. In most cases, these additional preloads simply hit existing entries and add nothing new. Removing these functions avoids redundant preloads and eliminates the multi-hit issue. This patch removes these two functions. We tested process switching performance using the context_switch benchmark on POWER9/hash, and observed no regression. Without this patch: 129041 ops/sec With this patch: 129341 ops/sec We also measured SLB faults during boot, and the counts are essentially the same with and without this patch. SLB faults without this patch: 19727 SLB faults with this patch: 19786 Fixes: 5434ae7 ("powerpc/64s/hash: Add a SLB preload cache") cc: stable@vger.kernel.org Suggested-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Donet Tom <donettom@linux.ibm.com> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com> Link: https://patch.msgid.link/0ac694ae683494fe8cadbd911a1a5018d5d3c541.1761834163.git.ritesh.list@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
wrenix
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May 7, 2026
commit a355eef upstream. Currently, the initialization of loongarch_jump_ops does not contain an assignment to its .free field. This causes disasm_line__free() to fall through to ins_ops__delete() for LoongArch jump instructions. ins_ops__delete() will free ins_operands.source.raw and ins_operands.source.name, and these fields overlaps with ins_operands.jump.raw_comment and ins_operands.jump.raw_func_start. Since in loongarch_jump__parse(), these two fields are populated by strchr()-ing the same buffer, trying to free them will lead to undefined behavior. This invalid free usually leads to crashes: Process 1712902 (perf) of user 1000 dumped core. Stack trace of thread 1712902: #0 0x00007fffef155c58 n/a (libc.so.6 + 0x95c58) sc7280-mainline#1 0x00007fffef0f7a94 raise (libc.so.6 + 0x37a94) sc7280-mainline#2 0x00007fffef0dd6a8 abort (libc.so.6 + 0x1d6a8) sc7280-mainline#3 0x00007fffef145490 n/a (libc.so.6 + 0x85490) sc7280-mainline#4 0x00007fffef1646f4 n/a (libc.so.6 + 0xa46f4) sc7280-mainline#5 0x00007fffef164718 n/a (libc.so.6 + 0xa4718) sc7280-mainline#6 0x00005555583a6764 __zfree (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x106764) sc7280-mainline#7 0x000055555854fb70 disasm_line__free (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x2afb70) sc7280-mainline#8 0x000055555853d618 annotated_source__purge (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x29d618) sc7280-mainline#9 0x000055555852300c __hist_entry__tui_annotate (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x28300c) sc7280-mainline#10 0x0000555558526718 do_annotate (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x286718) sc7280-mainline#11 0x000055555852ed94 evsel__hists_browse (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x28ed94) sc7280-mainline#12 0x000055555831fdd0 cmd_report (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x7fdd0) sc7280-mainline#13 0x000055555839b644 handle_internal_command (/home/csmantle/dist/linux-arch/tools/perf/perf + 0xfb644) sc7280-mainline#14 0x00005555582fe6ac main (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x5e6ac) sc7280-mainline#15 0x00007fffef0ddd90 n/a (libc.so.6 + 0x1dd90) sc7280-mainline#16 0x00007fffef0ddf0c __libc_start_main (libc.so.6 + 0x1df0c) sc7280-mainline#17 0x00005555582fed10 _start (/home/csmantle/dist/linux-arch/tools/perf/perf + 0x5ed10) ELF object binary architecture: LoongArch ... and it can be confirmed with Valgrind: ==1721834== Invalid free() / delete / delete[] / realloc() ==1721834== at 0x4EA9014: free (in /usr/lib/valgrind/vgpreload_memcheck-loongarch64-linux.so) ==1721834== by 0x4106287: __zfree (zalloc.c:13) ==1721834== by 0x42ADC8F: disasm_line__free (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x429B737: annotated_source__purge (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x42811EB: __hist_entry__tui_annotate (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x42848D7: do_annotate (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x428CF33: evsel__hists_browse (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== Address 0x7d34303 is 35 bytes inside a block of size 62 alloc'd ==1721834== at 0x4EA59B8: malloc (in /usr/lib/valgrind/vgpreload_memcheck-loongarch64-linux.so) ==1721834== by 0x6B80B6F: strdup (strdup.c:42) ==1721834== by 0x42AD917: disasm_line__new (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x42AE5A3: symbol__disassemble_objdump (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x42AF0A7: symbol__disassemble (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x429B3CF: symbol__annotate (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x429C233: symbol__annotate2 (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x42804D3: __hist_entry__tui_annotate (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x42848D7: do_annotate (in /home/csmantle/dist/linux-arch/tools/perf/perf) ==1721834== by 0x428CF33: evsel__hists_browse (in /home/csmantle/dist/linux-arch/tools/perf/perf) This patch adds the missing free() specialization in loongarch_jump_ops, which prevents disasm_line__free() from invoking the default cleanup function. Fixes: fb7fd2a ("perf annotate: Move raw_comment and raw_func_start fields out of 'struct ins_operands'") Cc: stable@vger.kernel.org Cc: WANG Rui <wangrui@loongson.cn> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: WANG Xuerui <kernel@xen0n.name> Cc: loongarch@lists.linux.dev Signed-off-by: Rong Bao <rong.bao@csmantle.top> Tested-by: WANG Rui <wangrui@loongson.cn> Signed-off-by: Namhyung Kim <namhyung@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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The downstream dts still has this at 2.5MiB unlike counterparts such as the Fairphone 5 who set it to 6MiB
https://github.com/SHIFTPHONES/android_kernel_shift_qcm6490/blob/5b43ded8bf11d1d0571ade9979ffee03f9a0b973/arch/arm64/boot/dts/vendor/qcom/yupik.dtsi#L4680