On Thu, Jun 23, 2016 at 07:30:15PM +0800, Dennis Chen wrote: > This is a rework patch based on [1]. According to the proposal from > Mark Rutland, when applying the system memory limit through 'mem=x' > kernel command line, don't remove the rest memory regions above the > limit from the memblock, instead marking them as MEMBLOCK_NOMAP region, > which will preserve the ability to identify regions as normal memory > while not using them for allocation and the linear map. > > Without this patch, the ACPI core will map those acpi data regions(if > they are above the limit) as device type memory, which will result in > the alignment exception when ACPI core parses the AML data stream > since the parsing will produce some non-alignment accesses. > > [1]:http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/438443.html Please rewrite the message to be standalone (i.e. so peopel can read this without having to folow the link). Explain why using mem= makes ACPI think regions should be mapped as Device memory, the problems this causes for ACPICA, then cover why we want to nomap the region. > Signed-off-by: Dennis Chen <dennis.chen@xxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Steve Capper <steve.capper@xxxxxxx> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Cc: Will Deacon <will.deacon@xxxxxxx> > Cc: Mark Rutland <mark.rutland@xxxxxxx> > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> > Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: linux-acpi@xxxxxxxxxxxxxxx > Cc: linux-efi@xxxxxxxxxxxxxxx > --- > arch/arm64/mm/init.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index d45f862..e509e24 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -222,12 +222,14 @@ void __init arm64_memblock_init(void) > > /* > * Apply the memory limit if it was set. Since the kernel may be loaded > - * high up in memory, add back the kernel region that must be accessible > - * via the linear mapping. > + * in the memory regions above the limit, so we need to clear the > + * MEMBLOCK_NOMAP flag of this region to make it can be accessible via > + * the linear mapping. > */ > if (memory_limit != (phys_addr_t)ULLONG_MAX) { > - memblock_enforce_memory_limit(memory_limit); > - memblock_add(__pa(_text), (u64)(_end - _text)); > + memblock_mem_limit_mark_nomap(memory_limit); > + if (!memblock_is_map_memory(__pa(_text))) > + memblock_clear_nomap(__pa(_text), (u64)(_end - _text)); I think that the memblock_is_map_memory() check should go. Just because a page of the kernel image is mapped doesn't mean that the rest is. That will make this a 1-1 change. Other than that, this looks right to me. Thanks, Mark. > } > > if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) { > -- > 1.8.3.1 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>