On Tue, 7 Jun 2022 at 14:22, David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 07.06.22 11:38, Wupeng Ma wrote:
> > From: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> >
> > Initrd memory will be removed and then added in arm64_memblock_init() and this
> > will cause it to lose all of its memblock flags. The lost of MEMBLOCK_MIRROR
> > flag will lead to error log printed by find_zone_movable_pfns_for_nodes if
> > the lower 4G range has some non-mirrored memory.
> >
> > In order to solve this problem, the lost MEMBLOCK_MIRROR flag will be
> > reinstalled if the origin memblock has this flag.
> >
> > Signed-off-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
> > ---
> > arch/arm64/mm/init.c | 9 +++++++++
> > include/linux/memblock.h | 1 +
> > mm/memblock.c | 20 ++++++++++++++++++++
> > 3 files changed, 30 insertions(+)
> >
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 339ee84e5a61..11641f924d08 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -350,9 +350,18 @@ void __init arm64_memblock_init(void)
> > "initrd not fully accessible via the linear mapping -- please check your bootloader ...\n")) {
> > phys_initrd_size = 0;
> > } else {
> > + int flags, ret;
> > +
> > + ret = memblock_get_flags(base, &flags);
> > + if (ret)
> > + flags = 0;
> > +
> > memblock_remove(base, size); /* clear MEMBLOCK_ flags */
> > memblock_add(base, size);
> > memblock_reserve(base, size);
>
> Can you explain why we're removing+re-adding here exactly? Is it just to
> clear flags as the comment indicates?
>
This should only happen if the placement of the initrd conflicts with
a mem= command line parameter or it is not covered by memblock for
some other reason.
IOW, this should never happen, and if re-memblock_add'ing this memory
unconditionally is causing problems, we should fix that instead of
working around it.
> If it's really just about clearing flags, I wonder if we rather want to
> have an interface that does exactly that, and hides the way this is
> actually implemented (obtain flags, remove, re-add ...), internally.
>
> But most probably there is more magic in the code and clearing flags
> isn't all it ends up doing.
>
I don't remember exactly why we needed to clear the flags, but I think
it had to do with some corner case we hit when the initrd was
partially covered.
