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b=nXvEGBMtNl8qgI84IB/MXFyHvTle71fwMSR3UZk245lcu+k8fPcRrYLtvKLoPkmZ+ UMhhnIYbBWHDAe+dGhQh2Z5JL6VE6xoOWQUtUSSaVyLle30l1+udz8Y702tD4XihlR vj1aoLqgE7M4z3vTJxJM2Nu/C05GMMO+qLAXD3Br8hdHIAS+3+zOGWgrAJPpc4xQcc nv/b0iwf/33qIWhL83e6CWzozC4m81q0kXxlFm6q7gvMqKC9V2ZRYeTG6W/G6vwlAV TT9Po0BUmTTReeWVGEpK+lE4zFhJldWEFROfzm+GbsgXPKHij+cpa2iO+8cpT7CVn4 6r4e/BxzqiHYw== Date: Tue, 1 Sep 2026 21:49:45 +0300 From: Mike Rapoport To: Sang-Heon Jeon Cc: Andrew Morton , Jason Gunthorpe , linux-mm@kvack.org, Pratyush Yadav Subject: Re: [PATCH] memblock: fix page count when preserving reserve_mem regions Message-ID: References: <20260901165237.1025973-1-ekffu200098@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260901165237.1025973-1-ekffu200098@gmail.com> X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4CFA018000B X-Stat-Signature: fe1mgsoem7zkacegj1in65oe5a5hsxb6 X-HE-Tag: 1788288592-107546 X-HE-Meta: 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 tTVqnPOS ABgW/X+bjLqxkDhC8JIEMz8E6+3txNSwJxEzPiY9Emm7oduY+TH557x9IAiGFbYS0BuQ8xzWxOV5cRhIGm0FkC/Roil+jHxegESlPeO5b2tOGRZaFQyJBVMV92lH3wNl2inbjPfMufogP5RdsHoCSiJkAG8T1MEh/jDA1rM9bUCtl3hPtHK63ToGV9LD08hk42XvHSJ/aUpe+jSEGqFsxMKE4pznLeM9m79MULPPT24GMW8ZCXhMHmjwN5CA5lWR3QEkb1p/UlxvdbM3FfMsnX+RciB6gHHLxn1jeKhrqC7zGSxDj5o3eJx+C3pFX71zR4egp Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, On Wed, Sep 02, 2026 at 01:52:35AM +0900, Sang-Heon Jeon wrote: > When map->start or map->size is not page aligned, > reserved_mem_preserve() does not preserve the last pages of the region I believe it's the last page, not pages. > from map->start to map->start + map->size. > > After kexec the new kernel reserves only the preserved pages, so the > last pages are released to the buddy allocator. But > reserve_mem_find_by_name() still returns the whole region including the > last pages, so they can be allocated while the subsystem is still using > them. > > Preserve every page the region spans so the new kernel reserves all of > it. If there are two adjacent not page aligned reserve_mem regions, we'll preserve them twice, or worse unintentionally unpreserve one of them on error handling of another. I think it's better to restrict the reserve_mem alignment to PAGE_SIZE. > Fixes: 8375b76517cb ("kho: replace kho_preserve_phys() with kho_preserve_pages()") > Signed-off-by: Sang-Heon Jeon > --- > > QEMU-based test results > > - Booted with "memblock=debug kho=on reserve_mem=5000:64:oops" > > # kexec -s -l /bzImage --initrd=/initramfs.gz --reuse-cmdline > # kexec -e > # dmesg | grep kho_preserved_memory_reserve > > 1) AS-IS (before fix) > [ 0.188536] __memblock_reserve: [0x000000013ffee000-0x000000013ffeefff] nid=-1 flags=0 kho_preserved_memory_reserve+0x3d/0x70 > > 2) TO-BE (after fix) > [ 0.076935] __memblock_reserve: [0x000000013ffee000-0x000000013ffeffff] nid=-1 flags=0 kho_preserved_memory_reserve+0x3d/0x70 > > mm/memblock.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index 777c69f05400..a17b1cccaf3d 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -2534,7 +2534,8 @@ static int __init reserved_mem_preserve(void) > for (unsigned int i = 0; i < reserved_mem_count; i++, nr_preserved++) { > struct reserve_mem_table *map = &reserved_mem_table[i]; > struct page *page = phys_to_page(map->start); > - unsigned int nr_pages = map->size >> PAGE_SHIFT; > + unsigned int nr_pages = PFN_UP(map->start + map->size) - > + PFN_DOWN(map->start); > > err = kho_preserve_pages(page, nr_pages); > if (err) > @@ -2547,7 +2548,8 @@ static int __init reserved_mem_preserve(void) > for (unsigned int i = 0; i < nr_preserved; i++) { > struct reserve_mem_table *map = &reserved_mem_table[i]; > struct page *page = phys_to_page(map->start); > - unsigned int nr_pages = map->size >> PAGE_SHIFT; > + unsigned int nr_pages = PFN_UP(map->start + map->size) - > + PFN_DOWN(map->start); > > kho_unpreserve_pages(page, nr_pages); > } > > base-commit: dde94c26af59f5020adafafa08ece21ccd32590b > -- > 2.43.0 > -- Sincerely yours, Mike.