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Tue, 11 Nov 2025 01:05:11 -0800 (PST) MIME-Version: 1.0 References: <96559d5a8e897f97879259bad3117db617e21377.1761763681.git.m.wieczorretman@pm.me> In-Reply-To: <96559d5a8e897f97879259bad3117db617e21377.1761763681.git.m.wieczorretman@pm.me> From: Alexander Potapenko Date: Tue, 11 Nov 2025 10:04:34 +0100 X-Gm-Features: AWmQ_bnTIARw6amUs-gvSQivLCgG0XY32k4ioUAxykbqmf67HMroMwsIF2IdVwY Message-ID: Subject: Re: [PATCH v6 13/18] x86/mm: LAM initialization To: Maciej Wieczor-Retman Cc: xin@zytor.com, peterz@infradead.org, kaleshsingh@google.com, kbingham@kernel.org, akpm@linux-foundation.org, nathan@kernel.org, ryabinin.a.a@gmail.com, dave.hansen@linux.intel.com, bp@alien8.de, morbo@google.com, jeremy.linton@arm.com, smostafa@google.com, kees@kernel.org, baohua@kernel.org, vbabka@suse.cz, justinstitt@google.com, wangkefeng.wang@huawei.com, leitao@debian.org, jan.kiszka@siemens.com, fujita.tomonori@gmail.com, hpa@zytor.com, urezki@gmail.com, ubizjak@gmail.com, ada.coupriediaz@arm.com, nick.desaulniers+lkml@gmail.com, ojeda@kernel.org, brgerst@gmail.com, elver@google.com, pankaj.gupta@amd.com, mark.rutland@arm.com, trintaeoitogc@gmail.com, jpoimboe@kernel.org, thuth@redhat.com, pasha.tatashin@soleen.com, dvyukov@google.com, jhubbard@nvidia.com, catalin.marinas@arm.com, yeoreum.yun@arm.com, mhocko@suse.com, lorenzo.stoakes@oracle.com, samuel.holland@sifive.com, vincenzo.frascino@arm.com, bigeasy@linutronix.de, surenb@google.com, ardb@kernel.org, Liam.Howlett@oracle.com, nicolas.schier@linux.dev, ziy@nvidia.com, kas@kernel.org, tglx@linutronix.de, mingo@redhat.com, broonie@kernel.org, corbet@lwn.net, andreyknvl@gmail.com, maciej.wieczor-retman@intel.com, david@redhat.com, maz@kernel.org, rppt@kernel.org, will@kernel.org, luto@kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, linux-doc@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: CE9201C0011 X-Stat-Signature: q546ue4nzocff5dcgutpeqyz6r9tus8w X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1762851912-610745 X-HE-Meta: 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 qyJE1IqV 0/KVITxg295ZfJiU= 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, Oct 29, 2025 at 9:08=E2=80=AFPM Maciej Wieczor-Retman wrote: > > From: Maciej Wieczor-Retman > > To make use of KASAN's tag based mode on x86, Linear Address Masking > (LAM) needs to be enabled. To do that the 28th bit in CR4 has to be set. > > Set the bit in early memory initialization. > > When launching secondary CPUs the LAM bit gets lost. To avoid this add > it in a mask in head_64.S. The bitmask permits some bits of CR4 to pass > from the primary CPU to the secondary CPUs without being cleared. > > Signed-off-by: Maciej Wieczor-Retman Acked-by: Alexander Potapenko