linux-kernel - [PATCH 1/1] mm: Always release pages to the buddy allocator in memblock_free

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Message-ID: <010101857bbc4d26-d9683bb4-c4f0-465b-aea6-5314dbf0aa01-000000@us-west-2.amazonses.com>
Date:   Wed, 4 Jan 2023 07:43:36 +0000
From:   Aaron Thompson <dev@...ont.org>
To:     linux-mm@...ck.org, Mike Rapoport <rppt@...nel.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andy@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Darren Hart <dvhart@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Marco Elver <elver@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        kasan-dev@...glegroups.com, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        x86@...nel.org, Aaron Thompson <dev@...ont.org>
Subject: [PATCH 1/1] 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. memblock_free_all() initializes all pages in reserved ranges, 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.

Fixes: 3a80a7fa7989 ("mm: meminit: initialise a subset of struct pages if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set")
Signed-off-by: Aaron Thompson <dev@...ont.org>
---
 mm/memblock.c                     | 2 +-
 tools/testing/memblock/internal.h | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 511d4783dcf1..56a5b6086c50 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1640,7 +1640,7 @@ 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);
+		__free_pages_core(pfn_to_page(cursor), 0);
 		totalram_pages_inc();
 	}
 }
diff --git a/tools/testing/memblock/internal.h b/tools/testing/memblock/internal.h
index fdb7f5db7308..85973e55489e 100644
--- a/tools/testing/memblock/internal.h
+++ b/tools/testing/memblock/internal.h
@@ -15,6 +15,10 @@ bool mirrored_kernelcore = false;

 struct page {};

+void __free_pages_core(struct page *page, unsigned int order)
+{
+}
+
 void memblock_free_pages(struct page *page, unsigned long pfn,
 			 unsigned int order)
 {
-- 
2.30.2