On 26/01/2026 09:26, Ard Biesheuvel wrote: > From: Ard Biesheuvel <[email protected]> > > Now that the DRAM mapping routines respect existing table mappings and > contiguous block and page mappings, it is no longer needed to fiddle > with the memblock tables to set and clear the NOMAP attribute. Instead, > map the kernel text and rodata alias first, avoiding contiguous > mappings, so that they will not be added later when mapping the > memblocks.
Should we do something similar for kfence? Currently we have arm64_kfence_alloc_pool() which marks some memory NOMAP then arm64_kfence_map_pool() which PTE-maps it and clears NOMAP. Presumably we could rationalize into a single function that does it all, prior to mapping the bulk of the linear map? > > Signed-off-by: Ard Biesheuvel <[email protected]> > --- > arch/arm64/mm/mmu.c | 27 ++++++++------------ > 1 file changed, 10 insertions(+), 17 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 80587cd47ce7..18415d4743bf 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1149,12 +1149,17 @@ static void __init map_mem(void) > flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; > > /* > - * Take care not to create a writable alias for the > - * read-only text and rodata sections of the kernel image. > - * So temporarily mark them as NOMAP to skip mappings in > - * the following for-loop > + * Map the linear alias of the [_text, __init_begin) interval > + * as non-executable now, and remove the write permission in > + * mark_linear_text_alias_ro() above (which will be called after > + * alternative patching has completed). This makes the contents > + * of the region accessible to subsystems such as hibernate, > + * but protects it from inadvertent modification or execution. > + * Note that contiguous mappings cannot be remapped in this way, > + * so we should avoid them here. > */ > - memblock_mark_nomap(kernel_start, kernel_end - kernel_start); > + __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, > + flags | NO_CONT_MAPPINGS); So the reason to disallow cont mappings is because we need to modify the permissions later? It _is_ safe to change permissions on a live contiguous mapping in this way. That was clarified in the architecture a couple of years back and we rely on it for contpte_wrprotect_ptes(); see comment there. I think we could relax this? Thanks, Ryan > > /* map all the memory banks */ > for_each_mem_range(i, &start, &end) { > @@ -1167,18 +1172,6 @@ static void __init map_mem(void) > flags); > } > > - /* > - * Map the linear alias of the [_text, __init_begin) interval > - * as non-executable now, and remove the write permission in > - * mark_linear_text_alias_ro() below (which will be called after > - * alternative patching has completed). This makes the contents > - * of the region accessible to subsystems such as hibernate, > - * but protects it from inadvertent modification or execution. > - * Note that contiguous mappings cannot be remapped in this way, > - * so we should avoid them here. > - */ > - __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, NO_CONT_MAPPINGS); > - memblock_clear_nomap(kernel_start, kernel_end - kernel_start); > arm64_kfence_map_pool(early_kfence_pool); > } >
