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Wed, 11 Nov 2020 15:27:18 -0800 (PST) Date: Thu, 12 Nov 2020 00:27:13 +0100 From: Marco Elver To: Andrey Konovalov Cc: Dmitry Vyukov , Alexander Potapenko , Catalin Marinas , Will Deacon , Vincenzo Frascino , Evgenii Stepanov , Andrey Ryabinin , Branislav Rankov , Kevin Brodsky , Andrew Morton , kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 19/20] kasan, mm: allow cache merging with no metadata Message-ID: <20201111232713.GA1244863@elver.google.com> References: <936c0c198145b663e031527c49a6895bd21ac3a0.1605046662.git.andreyknvl@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <936c0c198145b663e031527c49a6895bd21ac3a0.1605046662.git.andreyknvl@google.com> User-Agent: Mutt/1.14.6 (2020-07-11) Content-Transfer-Encoding: quoted-printable 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 Tue, Nov 10, 2020 at 11:20PM +0100, Andrey Konovalov wrote: > The reason cache merging is disabled with KASAN is because KASAN puts i= ts > metadata right after the allocated object. When the merged caches have > slightly different sizes, the metadata ends up in different places, whi= ch > KASAN doesn't support. >=20 > It might be possible to adjust the metadata allocation algorithm and ma= ke > it friendly to the cache merging code. Instead this change takes a simp= ler > approach and allows merging caches when no metadata is present. Which i= s > the case for hardware tag-based KASAN with kasan.mode=3Dprod. >=20 > Signed-off-by: Andrey Konovalov > Link: https://linux-review.googlesource.com/id/Ia114847dfb2244f297d2cb8= 2d592bf6a07455dba > --- > include/linux/kasan.h | 26 ++++++++++++++++++++++++-- > mm/kasan/common.c | 11 +++++++++++ > mm/slab_common.c | 11 ++++++++--- > 3 files changed, 43 insertions(+), 5 deletions(-) >=20 [...] > =20 > +/* > + * Only allow cache merging when stack collection is disabled and no m= etadata > + * is present. > + */ > +slab_flags_t __kasan_never_merge(slab_flags_t flags) I'm getting=20 mm/kasan/common.c:88:14: warning: no previous prototype for =E2=80=98__k= asan_never_merge=E2=80=99 [-Wmissing-prototypes]=20 for a KASAN x86 build with W=3D1. Presumably because if !KASAN_HW_TAGS then this is never needed and defined static inline in the header. > +{ > + if (kasan_stack_collection_enabled()) > + return flags; > + return flags & ~SLAB_KASAN; > +} Thanks, -- Marco