On Fri, May 29, 2026 at 05:02:02PM +0200, Ard Biesheuvel wrote: > From: Ard Biesheuvel <[email protected]> > > The only remaining use of map_patch_area() is mapping the zero page, and > immediately unmapping it again so that the intermediate page table > levels are all guaranteed to be populated. > > The use of the zero page here is completely arbitrary, and not harmful > per se, but currently, it creates a writable mapping, and does so in a > manner that requires that the empty_zero_page[] symbol is not > const-qualified. > > Given that this is about to change, and that map_patch_area() now never > maps anything other than the zero page, let's simplify the code and > - remove the helpers and call [un]map_kernel_page() directly > - take the PA of empty_zero_page directly > - create a read-only temporary mapping. > > This allows empty_zero_page[] to be repainted as const u8[] in a > subsequent patch, without making substantial changes to this code > patching logic. > > Cc: Madhavan Srinivasan <[email protected]> > Cc: Michael Ellerman <[email protected]> > Cc: Nicholas Piggin <[email protected]> > Cc: "Christophe Leroy (CS GROUP)" <[email protected]> > Link: https://lore.kernel.org/all/[email protected]/ > Signed-off-by: Ard Biesheuvel <[email protected]> > --- > arch/powerpc/lib/code-patching.c | 52 +------------------- > 1 file changed, 2 insertions(+), 50 deletions(-) > > diff --git a/arch/powerpc/lib/code-patching.c > b/arch/powerpc/lib/code-patching.c > index f84e0337cc02..44ff9f684bef 100644 > --- a/arch/powerpc/lib/code-patching.c > +++ b/arch/powerpc/lib/code-patching.c > @@ -60,9 +60,6 @@ struct patch_context { > > static DEFINE_PER_CPU(struct patch_context, cpu_patching_context); > > -static int map_patch_area(void *addr, unsigned long text_poke_addr); > -static void unmap_patch_area(unsigned long addr); > - > static bool mm_patch_enabled(void) > { > return IS_ENABLED(CONFIG_SMP) && radix_enabled(); > @@ -117,11 +114,11 @@ static int text_area_cpu_up(unsigned int cpu) > > // Map/unmap the area to ensure all page tables are pre-allocated > addr = (unsigned long)area->addr; > - err = map_patch_area(empty_zero_page, addr); > + err = map_kernel_page(addr, __pa_symbol(empty_zero_page), > PAGE_KERNEL_RO); > if (err) > return err; > > - unmap_patch_area(addr); > + unmap_kernel_page(addr); > > this_cpu_write(cpu_patching_context.area, area); > this_cpu_write(cpu_patching_context.addr, addr); > @@ -233,51 +230,6 @@ static unsigned long get_patch_pfn(void *addr) > return __pa_symbol(addr) >> PAGE_SHIFT; > } > > -/* > - * This can be called for kernel text or a module. > - */ > -static int map_patch_area(void *addr, unsigned long text_poke_addr) > -{ > - unsigned long pfn = get_patch_pfn(addr); > - > - return map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), > PAGE_KERNEL); > -} > - > -static void unmap_patch_area(unsigned long addr) > -{ > - pte_t *ptep; > - pmd_t *pmdp; > - pud_t *pudp; > - p4d_t *p4dp; > - pgd_t *pgdp; > - > - pgdp = pgd_offset_k(addr); > - if (WARN_ON(pgd_none(*pgdp))) > - return; > - > - p4dp = p4d_offset(pgdp, addr); > - if (WARN_ON(p4d_none(*p4dp))) > - return; > - > - pudp = pud_offset(p4dp, addr); > - if (WARN_ON(pud_none(*pudp))) > - return; > - > - pmdp = pmd_offset(pudp, addr); > - if (WARN_ON(pmd_none(*pmdp))) > - return; > - > - ptep = pte_offset_kernel(pmdp, addr); > - if (WARN_ON(pte_none(*ptep))) > - return; > - > - /* > - * In hash, pte_clear flushes the tlb, in radix, we have to > - */ > - pte_clear(&init_mm, addr, ptep); > - flush_tlb_kernel_range(addr, addr + PAGE_SIZE); > -} > - > static int __do_patch_mem_mm(void *addr, unsigned long val, bool is_dword) > { > int err; > -- > 2.54.0.823.g6e5bcc1fc9-goog > I don't see any functional change.
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
