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Howlett" , John Hubbard , Naoya Horiguchi , Hugh Dickins , Suren Baghdasaryan , Alex Sierra , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: extend max struct page size for kmsan Message-ID: References: <20230130130739.563628-1-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230130130739.563628-1-arnd@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 43E2312001B X-Stat-Signature: y7x7zgtcfoi91qsxzahppwexcqiynrgk X-HE-Tag: 1675085903-929181 X-HE-Meta: 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 RZ2fImKO sxgGP8PgDTQHXlPExwogvPolZXdCzIvl2NrEAZsEluDy5226WYxWPJZyQ7qfMHIdmdGau8Xg3pahlTsImpTrJS2GHYC7v0fRlHtU8FD0s2nvE670TuqhNyt2e39h0SiwISYao/t9xhGPMzEM/8B8wMbJ1vMShmUwT22wjwzCyWFAYHKhUigh72lrd55+yV/jBAiIZKJBUIfpo+qfwVp09fSXMJ8GvMSC6NXn+Qm+OT5M7plAoISOYpx7SQ+E6mQowOmDLI9tj9Qxtv7BqF491ZeLP/EAYHSjQwz8b7LfqOBBN7KLeptYJjZKZYg== 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: On Mon 30-01-23 14:07:26, Arnd Bergmann wrote: > From: Arnd Bergmann > > After x86 has enabled support for KMSAN, it has become possible > to have larger 'struct page' than was expected when commit > 5470dea49f53 ("mm: use mm_zero_struct_page from SPARC on all 64b > architectures") was merged: > > include/linux/mm.h:156:10: warning: no case matching constant switch condition '96' > switch (sizeof(struct page)) { > > Extend the maximum accordingly. > > Fixes: 5470dea49f53 ("mm: use mm_zero_struct_page from SPARC on all 64b architectures") > Fixes: 4ca8cc8d1bbe ("x86: kmsan: enable KMSAN builds for x86") > Signed-off-by: Arnd Bergmann Acked-by: Michal Hocko I haven't really followed KMSAN development but I would have expected that it would, like other debugging tools, add its metadata to page_ext rather than page directly. > --- > This seems to show up extremely rarely in randconfig builds, but > enough to trigger my build machine. > > I saw a related discussion at [1] about raising MAX_STRUCT_PAGE_SIZE, > but as I understand it, that needs to be addressed separately. > > [1] https://lore.kernel.org/lkml/20220701142310.2188015-11-glider@google.com/ > --- > include/linux/mm.h | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index b73ba2e5cfd2..aa39d5ddace1 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -137,7 +137,7 @@ extern int mmap_rnd_compat_bits __read_mostly; > * define their own version of this macro in > */ > #if BITS_PER_LONG == 64 > -/* This function must be updated when the size of struct page grows above 80 > +/* This function must be updated when the size of struct page grows above 96 > * or reduces below 56. The idea that compiler optimizes out switch() > * statement, and only leaves move/store instructions. Also the compiler can > * combine write statements if they are both assignments and can be reordered, > @@ -148,12 +148,18 @@ static inline void __mm_zero_struct_page(struct page *page) > { > unsigned long *_pp = (void *)page; > > - /* Check that struct page is either 56, 64, 72, or 80 bytes */ > + /* Check that struct page is either 56, 64, 72, 80, 88 or 96 bytes */ > BUILD_BUG_ON(sizeof(struct page) & 7); > BUILD_BUG_ON(sizeof(struct page) < 56); > - BUILD_BUG_ON(sizeof(struct page) > 80); > + BUILD_BUG_ON(sizeof(struct page) > 96); > > switch (sizeof(struct page)) { > + case 96: > + _pp[11] = 0; > + fallthrough; > + case 88: > + _pp[10] = 0; > + fallthrough; > case 80: > _pp[9] = 0; > fallthrough; > -- > 2.39.0 -- Michal Hocko SUSE Labs