From: Tianyang Zhang <zhangtianyang@loongson.cn> linux-next inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IC6CVG CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?... -------------------------------- When CONFIG_PREEMPT_COUNT is not configured (i.e. CONFIG_PREEMPT_NONE/ CONFIG_PREEMPT_VOLUNTARY), preempt_disable() / preempt_enable() merely acts as a barrier(). However, in these cases cond_resched() can still trigger a context switch and modify the CSR.EUEN, resulting in do_fpu() exception being activated within the kernel-fpu critical sections, as demonstrated in the following path: dcn32_calculate_wm_and_dlg() DC_FP_START() dcn32_calculate_wm_and_dlg_fpu() dcn32_find_dummy_latency_index_for_fw_based_mclk_switch() dcn32_internal_validate_bw() dcn32_enable_phantom_stream() dc_create_stream_for_sink() kzalloc(GFP_KERNEL) __kmem_cache_alloc_node() __cond_resched() DC_FP_END() This patch is similar to commit d02198550423 ("x86/fpu: Improve crypto performance by making kernel-mode FPU reliably usable in softirqs"). It uses local_bh_disable() instead of preempt_disable() for non-RT kernels so it can avoid the cond_resched() issue, and also extend the kernel-fpu application scenarios to the softirq context. Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn> Signed-off-by: Hongchen Zhang <zhanghongchen@loongson.cn> --- arch/loongarch/kernel/kfpu.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/arch/loongarch/kernel/kfpu.c b/arch/loongarch/kernel/kfpu.c index ec5b28e570c9..4c476904227f 100644 --- a/arch/loongarch/kernel/kfpu.c +++ b/arch/loongarch/kernel/kfpu.c @@ -18,11 +18,28 @@ static unsigned int euen_mask = CSR_EUEN_FPEN; static DEFINE_PER_CPU(bool, in_kernel_fpu); static DEFINE_PER_CPU(unsigned int, euen_current); +static inline void fpregs_lock(void) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); + else + local_bh_disable(); +} + +static inline void fpregs_unlock(void) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable(); + else + local_bh_enable(); +} + void kernel_fpu_begin(void) { unsigned int *euen_curr; - preempt_disable(); + if (!irqs_disabled()) + fpregs_lock(); WARN_ON(this_cpu_read(in_kernel_fpu)); @@ -73,7 +90,8 @@ void kernel_fpu_end(void) this_cpu_write(in_kernel_fpu, false); - preempt_enable(); + if (!irqs_disabled()) + fpregs_unlock(); } EXPORT_SYMBOL_GPL(kernel_fpu_end); -- 2.33.0