From: Sebastian Andrzej Siewior Date: Wed, 25 Jul 2018 14:02:38 +0200 Subject: [PATCH] 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-4.19.1-rt3.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 --- arch/arm64/kernel/fpsimd.c | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -159,6 +159,16 @@ static void sve_free(struct task_struct __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 @@ -547,6 +557,7 @@ int sve_set_vector_length(struct task_st * non-SVE thread. */ if (task == current) { + preempt_disable(); local_bh_disable(); fpsimd_save(); @@ -557,8 +568,10 @@ int sve_set_vector_length(struct task_st 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 @@ -813,6 +826,7 @@ asmlinkage void do_sve_acc(unsigned int sve_alloc(current); + preempt_disable(); local_bh_disable(); fpsimd_save(); @@ -826,6 +840,7 @@ asmlinkage void do_sve_acc(unsigned int WARN_ON(1); /* SVE access shouldn't have trapped */ local_bh_enable(); + preempt_enable(); } /* @@ -892,10 +907,12 @@ void fpsimd_thread_switch(struct task_st void fpsimd_flush_thread(void) { int vl, supported_vl; + void *mem = NULL; if (!system_supports_fpsimd()) return; + preempt_disable(); local_bh_disable(); memset(¤t->thread.uw.fpsimd_state, 0, @@ -904,7 +921,7 @@ 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. @@ -940,6 +957,8 @@ void fpsimd_flush_thread(void) set_thread_flag(TIF_FOREIGN_FPSTATE); local_bh_enable(); + preempt_enable(); + kfree(mem); } /* @@ -951,9 +970,11 @@ void fpsimd_preserve_current_state(void) if (!system_supports_fpsimd()) return; + preempt_disable(); local_bh_disable(); fpsimd_save(); local_bh_enable(); + preempt_enable(); } /* @@ -1011,6 +1032,7 @@ void fpsimd_restore_current_state(void) if (!system_supports_fpsimd()) return; + preempt_disable(); local_bh_disable(); if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { @@ -1019,6 +1041,7 @@ void fpsimd_restore_current_state(void) } local_bh_enable(); + preempt_enable(); } /* @@ -1031,6 +1054,7 @@ void fpsimd_update_current_state(struct if (!system_supports_fpsimd()) return; + preempt_disable(); local_bh_disable(); current->thread.uw.fpsimd_state = *state; @@ -1043,6 +1067,7 @@ void fpsimd_update_current_state(struct clear_thread_flag(TIF_FOREIGN_FPSTATE); local_bh_enable(); + preempt_enable(); } /* @@ -1088,6 +1113,7 @@ void kernel_neon_begin(void) BUG_ON(!may_use_simd()); + preempt_disable(); local_bh_disable(); __this_cpu_write(kernel_neon_busy, true); @@ -1101,6 +1127,7 @@ void kernel_neon_begin(void) preempt_disable(); local_bh_enable(); + preempt_enable(); } EXPORT_SYMBOL(kernel_neon_begin);