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b=Ju8TW1WScXt7+y9B+mBjAUjPB6rGDTaKFMxURMULY0VyrjYthHysu2s88SjtAJQpG mzP4tBVg1zaZTFh3yqoccghCFL1QjSbWjaZW1CqldgddDSlBbXb/wMHtWCZpKSSwRc 2X4S0ARuzdLtzIs1qqD7yN6tNmCSlr0WGuJgPHrAvYLhbrowIQMhFv8rTsEgQX/OiR aJfA6WGjh5POC9hS56bLHgvApJENr5TlMIYpqBE6VkavRK1t2V1THv+eYVAFXXZGbr cneR41EUGbtu7cVpMgoh4iQL76Hf0VIQhO4XX1hV1Ol/GApYf7QyTHTD91FKkg4q03 uc22WkIx6j9sw== Date: Wed, 17 Sep 2025 17:20:03 +0300 From: Mike Rapoport To: David Hildenbrand Cc: Alexander Potapenko , akpm@linux-foundation.org, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, elver@google.com, dvyukov@google.com, kasan-dev@googlegroups.com, Aleksandr Nogikh Subject: Re: [PATCH v1] mm/memblock: Correct totalram_pages accounting with KMSAN Message-ID: References: <20250917123250.3597556-1-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 7572A40011 X-Stat-Signature: kxouxi5fr9wno6pdwfqkr35a33cqu7un X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1758118811-381966 X-HE-Meta: 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 wwDE6NFP Qlp4XEiSglzYGoiDsJC3q9bhLsqY5WdKoDagNm6ypZPjuykUOj8FUXHp2AWWJfTe4Y4Ivcf/+Uq/mX/Z0wbczHPUBDsYbYXAuf1n0T7K653PPh9OyTKrNeYmD2ED51VhT0V2UJQK+LSif8v9yEEoX8LdMhI+7W9XRyhnj5c2Vt9jzxwXuiKGP3Gw6njyH3Tj2AIO1MFiVIhMsUYLT2DpAekFS5A+IOdg8NyPn05iI2f4jvwD2Ce3TL1TYv3plL5PA1hLYbRFYqFeozfROdJq2E73OaCioP2wJ0/W6IpPw6UdkAGQztOkAPN5/LyOTExYKFeKoAopo1VGQX+RM36YFfj3xxg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 17, 2025 at 03:29:51PM +0200, David Hildenbrand wrote: > On 17.09.25 14:32, Alexander Potapenko wrote: > > When KMSAN is enabled, `kmsan_memblock_free_pages()` can hold back pages > > for metadata instead of returning them to the early allocator. The callers, > > however, would unconditionally increment `totalram_pages`, assuming the > > pages were always freed. This resulted in an incorrect calculation of the > > total available RAM, causing the kernel to believe it had more memory than > > it actually did. > > > > This patch refactors `memblock_free_pages()` to return the number of pages > > it successfully frees. If KMSAN stashes the pages, the function now > > returns 0; otherwise, it returns the number of pages in the block. > > > > The callers in `memblock.c` have been updated to use this return value, > > ensuring that `totalram_pages` is incremented only by the number of pages > > actually returned to the allocator. This corrects the total RAM accounting > > when KMSAN is active. > > > > Cc: Aleksandr Nogikh > > Fixes: 3c2065098260 ("init: kmsan: call KMSAN initialization routines") > > Signed-off-by: Alexander Potapenko > > --- > > mm/internal.h | 4 ++-- > > mm/memblock.c | 18 +++++++++--------- > > mm/mm_init.c | 9 +++++---- > > 3 files changed, 16 insertions(+), 15 deletions(-) > > > > diff --git a/mm/internal.h b/mm/internal.h > > index 45b725c3dc030..ae1ee6e02eff9 100644 > > --- a/mm/internal.h > > +++ b/mm/internal.h > > @@ -742,8 +742,8 @@ static inline void clear_zone_contiguous(struct zone *zone) > > extern int __isolate_free_page(struct page *page, unsigned int order); > > extern void __putback_isolated_page(struct page *page, unsigned int order, > > int mt); > > -extern void memblock_free_pages(struct page *page, unsigned long pfn, > > - unsigned int order); > > +extern unsigned long memblock_free_pages(struct page *page, unsigned long pfn, > > + unsigned int order); > > extern void __free_pages_core(struct page *page, unsigned int order, > > enum meminit_context context); > > diff --git a/mm/memblock.c b/mm/memblock.c > > index 117d963e677c9..de7ff644d8f4f 100644 > > --- a/mm/memblock.c > > +++ b/mm/memblock.c > > @@ -1834,10 +1834,9 @@ void __init memblock_free_late(phys_addr_t base, phys_addr_t size) > > cursor = PFN_UP(base); > > end = PFN_DOWN(base + size); > > - for (; cursor < end; cursor++) { > > - memblock_free_pages(pfn_to_page(cursor), cursor, 0); > > - totalram_pages_inc(); > > - } > > + for (; cursor < end; cursor++) > > + totalram_pages_add( > > + memblock_free_pages(pfn_to_page(cursor), cursor, 0)); > > } > > That part is clear. But for readability we should probably just do > > if (memblock_free_pages(pfn_to_page(cursor), cursor, 0)) > totalram_pages_inc(); > > Or use a temp variable as an alternative. I prefer this one and totalram_pages_add() after the loop > LGTM > > Reviewed-by: David Hildenbrand > > -- > Cheers > > David / dhildenb > -- Sincerely yours, Mike.