| Message ID | 20220124170555.1054480-1-ardb@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: make 'highmem' symbol ro_after_init | expand |
On Mon, 24 Jan 2022, Ard Biesheuvel wrote: > 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); > > /* Same should be true for the mm/nommu.c variant?
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. I'm not against this patch, but it'd be nice to go further and remove it entirely for !CONFIG_HIGHMEM builds? Adding something like static inline bool is_high_pfn(unsigned long pfn) { #ifdef CONFIG_HIGHMEM return pfn <= max_low_pfn; #else return false; #endif } static inline bool is_high_phys(phys_addr_t pa) { return is_high_pfn(pa / PAGE_SIZE); } static inline bool is_high_addr(void *addr) { return is_high_phys(virt_to_phys(addr)); } should be all the primitives you need, from a quick grep. > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > 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 > >
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@kernel.org> Acked-by: Mike Rapoport <rppt@linux.ibm.com> > --- > 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 > >
On Wed, 26 Jan 2022 at 22:38, Mike Rapoport <rppt@kernel.org> 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@kernel.org> > > Acked-by: Mike Rapoport <rppt@linux.ibm.com> > > > --- > > 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.
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); /*
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@kernel.org> --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)