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Sat, 06 Sep 2025 10:18:51 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Andrey Konovalov Date: Sat, 6 Sep 2025 19:18:41 +0200 X-Gm-Features: AS18NWAE44l-F8fxYkxmWh2eLEtrt0fldHS7j-JrDWBIap-lKzv70eyY1F7Ln-M Message-ID: Subject: Re: [PATCH v5 12/19] x86: Minimal SLAB alignment To: Maciej Wieczor-Retman Cc: sohil.mehta@intel.com, baohua@kernel.org, david@redhat.com, kbingham@kernel.org, weixugc@google.com, Liam.Howlett@oracle.com, alexandre.chartre@oracle.com, kas@kernel.org, mark.rutland@arm.com, trintaeoitogc@gmail.com, axelrasmussen@google.com, yuanchu@google.com, joey.gouly@arm.com, samitolvanen@google.com, joel.granados@kernel.org, graf@amazon.com, vincenzo.frascino@arm.com, kees@kernel.org, ardb@kernel.org, thiago.bauermann@linaro.org, glider@google.com, thuth@redhat.com, kuan-ying.lee@canonical.com, pasha.tatashin@soleen.com, nick.desaulniers+lkml@gmail.com, vbabka@suse.cz, kaleshsingh@google.com, justinstitt@google.com, catalin.marinas@arm.com, alexander.shishkin@linux.intel.com, samuel.holland@sifive.com, dave.hansen@linux.intel.com, corbet@lwn.net, xin@zytor.com, dvyukov@google.com, tglx@linutronix.de, scott@os.amperecomputing.com, jason.andryuk@amd.com, morbo@google.com, nathan@kernel.org, lorenzo.stoakes@oracle.com, mingo@redhat.com, brgerst@gmail.com, kristina.martsenko@arm.com, bigeasy@linutronix.de, luto@kernel.org, jgross@suse.com, jpoimboe@kernel.org, urezki@gmail.com, mhocko@suse.com, ada.coupriediaz@arm.com, hpa@zytor.com, leitao@debian.org, peterz@infradead.org, wangkefeng.wang@huawei.com, surenb@google.com, ziy@nvidia.com, smostafa@google.com, ryabinin.a.a@gmail.com, ubizjak@gmail.com, jbohac@suse.cz, broonie@kernel.org, akpm@linux-foundation.org, guoweikang.kernel@gmail.com, rppt@kernel.org, pcc@google.com, jan.kiszka@siemens.com, nicolas.schier@linux.dev, will@kernel.org, jhubbard@nvidia.com, bp@alien8.de, x86@kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, linux-kbuild@vger.kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: dubf1zaorigxdkrkqjnwzpei4759xm81 X-Rspam-User: X-Rspamd-Queue-Id: 76B4B180003 X-Rspamd-Server: rspam01 X-HE-Tag: 1757179133-952141 X-HE-Meta: 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 Lp9w2bt3 PXIsgHJmjSGO/HrKIIOYj5Devc7C3iL5lDTxwMYS4arasB3w0BU6uDp0LPc54PbarFBbK8V+uS7Xrw/b97kW+NvyZ86uHTMVjF7lVhROGGKwQDkiuaeUwADGgbi9eS6vwZV1PppMA0whs1lsUVSY4iPBmaGhOh+1DwgJ3W3NI4gmiDMyiK1hBxSEKdCxYZrLzYtJm8tQTdB68610swGilRpavwQDRP3xrKOuV9pu+9GD6nkkKFYM+ZSBpayvgwaVJ1xBTW476Dh5bJPZHHhccro4LednBmHwhcLhg4pn8f51khU8ki1KfMQ+f3UOEd4qOB0zAQeisgrgmvlrt+ZaoGbT/RfnFjAfPIZsc8Ol1yy2hb0kUYOtb5Fpo0ae5bJLJvJWh3CuskUk3F0P4uIEv3Uj43Xga5+u8rxppNBQxn7KR4t0xBCXFrcVPMOB2Mq2t824d+IFfPaSU5JDw58pp7GB9rMHYjSg+K9+b 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 Mon, Aug 25, 2025 at 10:29=E2=80=AFPM Maciej Wieczor-Retman wrote: > > 8 byte minimal SLAB alignment interferes with KASAN's granularity of 16 > bytes. It causes a lot of out-of-bounds errors for unaligned 8 byte > allocations. > > Compared to a kernel with KASAN disabled, the memory footprint increases > because all kmalloc-8 allocations now are realized as kmalloc-16, which > has twice the object size. But more meaningfully, when compared to a > kernel with generic KASAN enabled, there is no difference. Because of > redzones in generic KASAN, kmalloc-8' and kmalloc-16' object size is the > same (48 bytes). So changing the minimal SLAB alignment of the tag-based > mode doesn't have any negative impact when compared to the other > software KASAN mode. > > Adjust x86 minimal SLAB alignment to match KASAN granularity size. > > Signed-off-by: Maciej Wieczor-Retman > --- > Changelog v4: > - Extend the patch message with some more context and impact > information. > > Changelog v3: > - Fix typo in patch message 4 -> 16. > - Change define location to arch/x86/include/asm/cache.c. > > arch/x86/include/asm/cache.h | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/include/asm/cache.h b/arch/x86/include/asm/cache.h > index 69404eae9983..3232583b5487 100644 > --- a/arch/x86/include/asm/cache.h > +++ b/arch/x86/include/asm/cache.h > @@ -21,4 +21,8 @@ > #endif > #endif > > +#ifdef CONFIG_KASAN_SW_TAGS > +#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > +#endif > + > #endif /* _ASM_X86_CACHE_H */ > -- > 2.50.1 > Reviewed-by: Andrey Konovalov