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Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by casper.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1fW12r-0007R2-Tb for linux-arm-kernel@lists.infradead.org; Thu, 21 Jun 2018 14:58:52 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A4FEE80D; Thu, 21 Jun 2018 07:58:34 -0700 (PDT) Received: from e103592.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 096613F246; Thu, 21 Jun 2018 07:58:32 -0700 (PDT) From: Dave Martin To: kvmarm@lists.cs.columbia.edu Subject: [RFC PATCH 01/16] arm64: fpsimd: Always set TIF_FOREIGN_FPSTATE on task state flush Date: Thu, 21 Jun 2018 15:57:25 +0100 Message-Id: <1529593060-542-2-git-send-email-Dave.Martin@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1529593060-542-1-git-send-email-Dave.Martin@arm.com> References: <1529593060-542-1-git-send-email-Dave.Martin@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180621_155846_227749_CFEE9E12 X-CRM114-Status: GOOD ( 16.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Okamoto Takayuki , Christoffer Dall , Ard Biesheuvel , Marc Zyngier , Catalin Marinas , Will Deacon , =?UTF-8?q?Alex=20Benn=C3=A9e?= , linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP This patch updates fpsimd_flush_task_state() to mirror the new semantics of fpsimd_flush_cpu_state(): both functions now implicitly set TIF_FOREIGN_FPSTATE to indicate that the task's FPSIMD state is not loaded into the cpu. As a side-effect, fpsimd_flush_task_state() now sets TIF_FOREIGN_FPSTATE even for non-running tasks. In the case of non-running tasks this is not useful but also harmless, because the flag is live only while the corresponding task is running. This function is not called from fast paths, so special-casing this for the task == current case is not really worth it. Compiler barriers previously present in restore_sve_fpsimd_context() are pulled into fpsimd_flush_task_state() so that it can be safely called with preemption enabled if necessary. Explicit calls to set TIF_FOREIGN_FPSTATE that accompany fpsimd_flush_task_state() calls and are now redundant are removed as appropriate. fpsimd_flush_task_state() is used to get exclusive access to the representation of the task's state via task_struct, for the purpose of replacing the state. Thus, the call to this function should happen before manipulating fpsimd_state or sve_state etc. in task_struct. Anomalous cases are reordered appropriately in order to make the code more consistent, although there should be no functional difference since these cases are protected by local_bh_disable() anyway. Signed-off-by: Dave Martin Reviewed-by: Alex BennĂ©e --- arch/arm64/kernel/fpsimd.c | 25 +++++++++++++++++++------ arch/arm64/kernel/signal.c | 5 ----- 2 files changed, 19 insertions(+), 11 deletions(-) diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index 84c68b1..6b1ddae 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -569,7 +569,6 @@ int sve_set_vector_length(struct task_struct *task, local_bh_disable(); fpsimd_save(); - set_thread_flag(TIF_FOREIGN_FPSTATE); } fpsimd_flush_task_state(task); @@ -835,12 +834,11 @@ asmlinkage void do_sve_acc(unsigned int esr, struct pt_regs *regs) local_bh_disable(); fpsimd_save(); - fpsimd_to_sve(current); /* Force ret_to_user to reload the registers: */ fpsimd_flush_task_state(current); - set_thread_flag(TIF_FOREIGN_FPSTATE); + fpsimd_to_sve(current); if (test_and_set_thread_flag(TIF_SVE)) WARN_ON(1); /* SVE access shouldn't have trapped */ @@ -917,9 +915,9 @@ void fpsimd_flush_thread(void) local_bh_disable(); + fpsimd_flush_task_state(current); memset(¤t->thread.uw.fpsimd_state, 0, sizeof(current->thread.uw.fpsimd_state)); - fpsimd_flush_task_state(current); if (system_supports_sve()) { clear_thread_flag(TIF_SVE); @@ -956,8 +954,6 @@ void fpsimd_flush_thread(void) current->thread.sve_vl_onexec = 0; } - set_thread_flag(TIF_FOREIGN_FPSTATE); - local_bh_enable(); } @@ -1066,12 +1062,29 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state) /* * Invalidate live CPU copies of task t's FPSIMD state + * + * This function may be called with preemption enabled. The barrier() + * ensures that the assignment to fpsimd_cpu is visible to any + * preemption/softirq that could race with set_tsk_thread_flag(), so + * that TIF_FOREIGN_FPSTATE cannot be spuriously re-cleared. + * + * The final barrier ensures that TIF_FOREIGN_FPSTATE is seen set by any + * subsequent code. */ void fpsimd_flush_task_state(struct task_struct *t) { t->thread.fpsimd_cpu = NR_CPUS; + + barrier(); + set_tsk_thread_flag(t, TIF_FOREIGN_FPSTATE); + + barrier(); } +/* + * Invalidate any task's FPSIMD state that is present on this cpu. + * This function must be called with softirqs disabled. + */ void fpsimd_flush_cpu_state(void) { __this_cpu_write(fpsimd_last_state.st, NULL); diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index 511af13..7636965 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -296,11 +296,6 @@ static int restore_sve_fpsimd_context(struct user_ctxs *user) */ fpsimd_flush_task_state(current); - barrier(); - /* From now, fpsimd_thread_switch() won't clear TIF_FOREIGN_FPSTATE */ - - set_thread_flag(TIF_FOREIGN_FPSTATE); - barrier(); /* From now, fpsimd_thread_switch() won't touch thread.sve_state */ sve_alloc(current);