On Sun, Jan 15, 2023 at 09:03:05AM +0000, Aaron Thompson wrote:
>
> On 2023-01-15 00:32, Mike Rapoport wrote:
> > On Sat, Jan 14, 2023 at 05:45:53PM +0100, gregkh@xxxxxxxxxxxxxxxxxxx
> > wrote:
> > >
> > > The patch below does not apply to the 5.15-stable tree.
> > > If someone wants it applied there, or to any other stable or longterm
> > > tree, then please email the backport, including the original git
> > > commit
> > > id to <stable@xxxxxxxxxxxxxxx>.
> >
> > The patch below applies to 5.15, 5.10 and 5.4.
>
> Thanks Mike. The code works as intended, but the commit message and the
> comments have some inaccuracies (changed function names, no KMSAN). Does
> that matter? I can send updated patches if so, just let me know.
It's up to stable folks, I think.
Greg?
> > As for 4.19 and 4.14, they still have bootmem/nobootmem so I'd rather
> > wouldn't touch them.
> >
> > From c292bd7e64214fcc78b7c72a9ccd3973dd19b7fb Mon Sep 17 00:00:00 2001
> > From: Aaron Thompson <dev@xxxxxxxxxx>
> > Date: Fri, 6 Jan 2023 22:22:44 +0000
> > Subject: [PATCH] mm: Always release pages to the buddy allocator in
> > memblock_free_late().
> >
> > If CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled, memblock_free_pages()
> > only releases pages to the buddy allocator if they are not in the
> > deferred range. This is correct for free pages (as defined by
> > for_each_free_mem_pfn_range_in_zone()) because free pages in the
> > deferred range will be initialized and released as part of the deferred
> > init process. memblock_free_pages() is called by memblock_free_late(),
> > which is used to free reserved ranges after memblock_free_all() has
> > run. All pages in reserved ranges have been initialized at that point,
> > and accordingly, those pages are not touched by the deferred init
> > process. This means that currently, if the pages that
> > memblock_free_late() intends to release are in the deferred range, they
> > will never be released to the buddy allocator. They will forever be
> > reserved.
> >
> > In addition, memblock_free_pages() calls kmsan_memblock_free_pages(),
> > which is also correct for free pages but is not correct for reserved
> > pages. KMSAN metadata for reserved pages is initialized by
> > kmsan_init_shadow(), which runs shortly before memblock_free_all().
> >
> > For both of these reasons, memblock_free_pages() should only be called
> > for free pages, and memblock_free_late() should call __free_pages_core()
> > directly instead.
> >
> > One case where this issue can occur in the wild is EFI boot on
> > x86_64. The x86 EFI code reserves all EFI boot services memory ranges
> > via memblock_reserve() and frees them later via memblock_free_late()
> > (efi_reserve_boot_services() and efi_free_boot_services(),
> > respectively). If any of those ranges happens to fall within the
> > deferred init range, the pages will not be released and that memory will
> > be unavailable.
> >
> > For example, on an Amazon EC2 t3.micro VM (1 GB) booting via EFI:
> >
> > v6.2-rc2:
> > # grep -E 'Node|spanned|present|managed' /proc/zoneinfo
> > Node 0, zone DMA
> > spanned 4095
> > present 3999
> > managed 3840
> > Node 0, zone DMA32
> > spanned 246652
> > present 245868
> > managed 178867
> >
> > v6.2-rc2 + patch:
> > # grep -E 'Node|spanned|present|managed' /proc/zoneinfo
> > Node 0, zone DMA
> > spanned 4095
> > present 3999
> > managed 3840
> > Node 0, zone DMA32
> > spanned 246652
> > present 245868
> > managed 222816 # +43,949 pages
> >
> > Fixes: 3a80a7fa7989 ("mm: meminit: initialise a subset of struct pages
> > if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set")
> > Signed-off-by: Aaron Thompson <dev@xxxxxxxxxx>
> > Link:
> > https://lore.kernel.org/r/01010185892de53e-e379acfb-7044-4b24-b30a-e2657c1ba989-000000@xxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
> > ---
> > mm/memblock.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index 2b7397781c99..838d59a74c65 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -1615,7 +1615,13 @@ void __init __memblock_free_late(phys_addr_t
> > base, phys_addr_t size)
> > end = PFN_DOWN(base + size);
> >
> > for (; cursor < end; cursor++) {
> > - memblock_free_pages(pfn_to_page(cursor), cursor, 0);
> > + /*
> > + * Reserved pages are always initialized by the end of
> > + * memblock_free_all() (by memmap_init() and, if deferred
> > + * initialization is enabled, memmap_init_reserved_pages()), so
> > + * these pages can be released directly to the buddy allocator.
> > + */
> > + __free_pages_core(pfn_to_page(cursor), 0);
> > totalram_pages_inc();
> > }
> > }
> > --
> > 2.35.1
> >
> >
> > > thanks,
> > >
> > > greg k-h
> > >
>
> Thanks,
> -- Aaron
--
Sincerely yours,
Mike.
