On Wed, May 13, 2026 at 10:53:08AM +0200, Ard Biesheuvel wrote: > > On Wed, 13 May 2026, at 10:50, Mike Rapoport wrote: > > On Tue, May 12, 2026 at 02:56:16PM +0200, Ard Biesheuvel wrote: > >> On Mon, 11 May 2026, at 16:40, Jann Horn wrote: > >> > On Mon, May 11, 2026 at 10:59 AM Ard Biesheuvel <[email protected]> wrote: > >> >> I think we should simply do something along the lines of the below, > >> >> considering that the size of a data object tends to correlate with > >> >> its minimum alignment. > >> >> > >> >> I do find it rather puzzling that the compiler emits empty_zero_page > >> >> *after* zero_page_pfn - ideally, we'd combine the below with > >> >> -fdata-sections so that the linker sees all individual objects, but > >> >> I suspect that would create some problems elsewhere. > >> >> > >> >> > >> >> --- a/include/asm-generic/vmlinux.lds.h > >> >> +++ b/include/asm-generic/vmlinux.lds.h > >> >> @@ -452,7 +452,7 @@ > >> >> #define RO_AFTER_INIT_DATA \ > >> >> . = ALIGN(8); \ > >> >> __start_ro_after_init = .; \ > >> >> - *(.data..ro_after_init) \ > >> >> + *(SORT_BY_ALIGNMENT(.data..ro_after_init)) \ > >> > > >> > Oh, neat, I didn't realize that's possible. That seems like a nicer > >> > approach... > >> > >> Neat but rather ineffective, unfortunately. (I don't see a size > >> difference with the arm64 defconfig kernel) > >> > >> Given that empty_zero_page only ever gets its address taken, we > >> might just move it into the linker script if that requires tweaking > >> anyway. We can just place it at the start of .rodata, which is > >> already page aligned on most architectures (and will become page > >> aligned unless EMPTY_ZERO_PAGE is #define'd by the arch linker > >> script to something else) > >> > >> > >> --- a/include/asm-generic/vmlinux.lds.h > >> +++ b/include/asm-generic/vmlinux.lds.h > >> @@ -472,6 +472,17 @@ > >> #endif > >> #endif > >> > >> +#ifndef EMPTY_ZERO_PAGE > >> +#ifndef __HAVE_COLOR_ZERO_PAGE > > > > I don't think we want let architectures that don't use colored zero pages > > redefine it. > > If it will be really required we can add the ability to redefine > > EMPTY_ZERO_PAGE later. > > > > I was actually intending to add use this for arm64 in the next patch. It > already has a reserved_pg_dir in .rodata which is page-sized (i.e., up > to 64k in size) and guaranteed to remain all zeroes, so empty_zero_page > could actually be an alias for that. This is what I had in a previous > revision, before you turned the empty_zero_page definition into common > code:
Works for me if from arm64 perspective that's ok :) > https://lore.kernel.org/all/[email protected]/ -- Sincerely yours, Mike.
