From be02aec36e38152c42cd01344a5d02cce54853df Mon Sep 17 00:00:00 2001
Message-Id: <be02aec36e38152c42cd01344a5d02cce54853df.1599166691.git.zanussi@kernel.org>
In-Reply-To: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
References: <56457dc415803c8abc5acb513ada877a79596f05.1599166690.git.zanussi@kernel.org>
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 25 Jul 2018 14:02:38 +0200
Subject: [PATCH 212/333] arm64: fpsimd: use preemp_disable in addition to
 local_bh_disable()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.142-rt63.tar.xz

In v4.16-RT I noticed a number of warnings from task_fpsimd_load(). The
code disables BH and expects that it is not preemptible. On -RT the
task remains preemptible but remains the same CPU. This may corrupt the
content of the SIMD registers if the task is preempted during
saving/restoring those registers.

Add preempt_disable()/enable() to enfore the required semantic on -RT.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/arm64/kernel/fpsimd.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 19c87b52c001..203245dad743 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -159,6 +159,16 @@ static void sve_free(struct task_struct *task)
 	__sve_free(task);
 }
 
+static void *sve_free_atomic(struct task_struct *task)
+{
+	void *sve_state = task->thread.sve_state;
+
+	WARN_ON(test_tsk_thread_flag(task, TIF_SVE));
+
+	task->thread.sve_state = NULL;
+	return sve_state;
+}
+
 /*
  * TIF_SVE controls whether a task can use SVE without trapping while
  * in userspace, and also the way a task's FPSIMD/SVE state is stored
@@ -549,6 +559,7 @@ int sve_set_vector_length(struct task_struct *task,
 	 * non-SVE thread.
 	 */
 	if (task == current) {
+		preempt_disable();
 		local_bh_disable();
 
 		fpsimd_save();
@@ -559,8 +570,10 @@ int sve_set_vector_length(struct task_struct *task,
 	if (test_and_clear_tsk_thread_flag(task, TIF_SVE))
 		sve_to_fpsimd(task);
 
-	if (task == current)
+	if (task == current) {
 		local_bh_enable();
+		preempt_enable();
+	}
 
 	/*
 	 * Force reallocation of task SVE state to the correct size
@@ -815,6 +828,7 @@ asmlinkage void do_sve_acc(unsigned int esr, struct pt_regs *regs)
 
 	sve_alloc(current);
 
+	preempt_disable();
 	local_bh_disable();
 
 	fpsimd_save();
@@ -828,6 +842,7 @@ asmlinkage void do_sve_acc(unsigned int esr, struct pt_regs *regs)
 		WARN_ON(1); /* SVE access shouldn't have trapped */
 
 	local_bh_enable();
+	preempt_enable();
 }
 
 /*
@@ -894,10 +909,12 @@ void fpsimd_thread_switch(struct task_struct *next)
 void fpsimd_flush_thread(void)
 {
 	int vl, supported_vl;
+	void *mem = NULL;
 
 	if (!system_supports_fpsimd())
 		return;
 
+	preempt_disable();
 	local_bh_disable();
 
 	memset(&current->thread.uw.fpsimd_state, 0,
@@ -906,7 +923,7 @@ void fpsimd_flush_thread(void)
 
 	if (system_supports_sve()) {
 		clear_thread_flag(TIF_SVE);
-		sve_free(current);
+		mem = sve_free_atomic(current);
 
 		/*
 		 * Reset the task vector length as required.
@@ -942,6 +959,8 @@ void fpsimd_flush_thread(void)
 	set_thread_flag(TIF_FOREIGN_FPSTATE);
 
 	local_bh_enable();
+	preempt_enable();
+	kfree(mem);
 }
 
 /*
@@ -953,9 +972,11 @@ void fpsimd_preserve_current_state(void)
 	if (!system_supports_fpsimd())
 		return;
 
+	preempt_disable();
 	local_bh_disable();
 	fpsimd_save();
 	local_bh_enable();
+	preempt_enable();
 }
 
 /*
@@ -1026,6 +1047,7 @@ void fpsimd_restore_current_state(void)
 		return;
 	}
 
+	preempt_disable();
 	local_bh_disable();
 
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
@@ -1034,6 +1056,7 @@ void fpsimd_restore_current_state(void)
 	}
 
 	local_bh_enable();
+	preempt_enable();
 }
 
 /*
@@ -1046,6 +1069,7 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state)
 	if (WARN_ON(!system_supports_fpsimd()))
 		return;
 
+	preempt_disable();
 	local_bh_disable();
 
 	current->thread.uw.fpsimd_state = *state;
@@ -1058,6 +1082,7 @@ void fpsimd_update_current_state(struct user_fpsimd_state const *state)
 	clear_thread_flag(TIF_FOREIGN_FPSTATE);
 
 	local_bh_enable();
+	preempt_enable();
 }
 
 /*
@@ -1104,6 +1129,7 @@ void kernel_neon_begin(void)
 
 	BUG_ON(!may_use_simd());
 
+	preempt_disable();
 	local_bh_disable();
 
 	__this_cpu_write(kernel_neon_busy, true);
@@ -1117,6 +1143,7 @@ void kernel_neon_begin(void)
 	preempt_disable();
 
 	local_bh_enable();
+	preempt_enable();
 }
 EXPORT_SYMBOL(kernel_neon_begin);
 
-- 
2.17.1

