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charset="utf-8" Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261107_073723_116309_EFE99904 X-CRM114-Status: GOOD ( 12.37 ) X-Spam-Score: -9.5 (---------) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-26.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIMWL_WL_MED,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT, USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 For performance reasons, kernel entry might skip clearing TCO. Still, tasks expecting synchronous uaccess tag faults to be reported (and therefore raised) require it to be clear; this is why thread switching and MTE enabling functions were calling into mte_disable_tco_entry(). However, when the kernel itself uses MTE (for KASAN), it must have cleared TCO on kernel entry. Use that invariant to skip redundantly clearing TCO and/or checking the task's SCTLR. As kasan_hw_tags_enabled() uses a static branch, TCO maintenance is completely optimized out the moment HW KASAN is enabled. Cc: Peter Collingbourne Signed-off-by: Pierre-Cl=C3=A9ment Tosi --- arch/arm64/kernel/mte.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index d1dd9b80173a..8025ee1f7fdb 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -5,6 +5,7 @@ =20 #include #include +#include #include #include #include @@ -290,7 +291,8 @@ void mte_thread_switch(struct task_struct *next) mte_update_gcr_excl(next); =20 /* TCO may not have been disabled on exception entry for the current task= . */ - mte_disable_tco_entry(next); + if (!kasan_hw_tags_enabled()) + mte_disable_tco_entry(next); =20 if (!system_uses_mte_async_or_asymm_mode()) return; @@ -409,7 +411,8 @@ long set_mte_ctrl(struct task_struct *task, unsigned lo= ng arg) mte_update_sctlr_user(task); mte_update_gcr_excl(task); update_sctlr_el1(task->thread.sctlr_user); - mte_disable_tco_entry(task); + if (!kasan_hw_tags_enabled()) + mte_disable_tco_entry(task); preempt_enable(); } =20 --=20 2.56.0.455.g6c5a503b38-goog