On Wed, 26 Jan 2022 at 22:38, Mike Rapoport <rppt@xxxxxxxxxx> wrote: > > On Mon, Jan 24, 2022 at 06:05:55PM +0100, Ard Biesheuvel wrote: > > The 'highmem' variable is only set at boot, so we can make it > > ro_after_init and prevent it from being corrupted inadvertently, or from > > ending up in a contended cacheline. > > > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > > --- > > mm/memory.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index c125c4969913..50e82cb94ccc 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -106,7 +106,7 @@ EXPORT_SYMBOL(mem_map); > > * highstart_pfn must be the same; there must be no gap between ZONE_NORMAL > > * and ZONE_HIGHMEM. > > */ > > -void *high_memory; > > +void *high_memory __ro_after_init; > > EXPORT_SYMBOL(high_memory); > > > > /* > > -- > > 2.30.2 > > > > > This turns out to break CONFIG_MEMORY_HOTPLUG on x86, as it updates max_pfn, max_low_pfn and high_memory after init. So probably best to make all of those __read_mostly instead.
