From 14e153ef75eecae8fd0738ffb42120f4962a00cd Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 15 Jan 2015 20:19:43 +0100 Subject: [PATCH] x86, fpu: Introduce per-cpu in_kernel_fpu state interrupted_kernel_fpu_idle() tries to detect if kernel_fpu_begin() is safe or not. In particular it should obviously deny the nested kernel_fpu_begin() and this logic looks very confusing. If use_eager_fpu() == T we rely on a) __thread_has_fpu() check in interrupted_kernel_fpu_idle(), and b) on the fact that _begin() does __thread_clear_has_fpu(). Otherwise we demand that the interrupted task has no FPU if it is in kernel mode, this works because __kernel_fpu_begin() does clts() and interrupted_kernel_fpu_idle() checks X86_CR0_TS. Add the per-cpu "bool in_kernel_fpu" variable, and change this code to check/set/clear it. This allows to do more cleanups and fixes, see the next changes. The patch also moves WARN_ON_ONCE() under preempt_disable() just to make this_cpu_read() look better, this is not really needed. And in fact I think we should move it into __kernel_fpu_begin(). Signed-off-by: Oleg Nesterov Reviewed-by: Rik van Riel Cc: matt.fleming@intel.com Cc: bp@suse.de Cc: pbonzini@redhat.com Cc: luto@amacapital.net Cc: Linus Torvalds Cc: Suresh Siddha Link: http://lkml.kernel.org/r/20150115191943.GB27332@redhat.com Signed-off-by: Thomas Gleixner --- arch/x86/include/asm/i387.h | 2 +- arch/x86/kernel/i387.c | 9 +++++++++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h index ed8089d69094..5e275d31802e 100644 --- a/arch/x86/include/asm/i387.h +++ b/arch/x86/include/asm/i387.h @@ -40,8 +40,8 @@ extern void __kernel_fpu_end(void); static inline void kernel_fpu_begin(void) { - WARN_ON_ONCE(!irq_fpu_usable()); preempt_disable(); + WARN_ON_ONCE(!irq_fpu_usable()); __kernel_fpu_begin(); } diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index a9a4229f6161..a81572338243 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -19,6 +19,8 @@ #include #include +static DEFINE_PER_CPU(bool, in_kernel_fpu); + /* * Were we in an interrupt that interrupted kernel mode? * @@ -33,6 +35,9 @@ */ static inline bool interrupted_kernel_fpu_idle(void) { + if (this_cpu_read(in_kernel_fpu)) + return false; + if (use_eager_fpu()) return __thread_has_fpu(current); @@ -73,6 +78,8 @@ void __kernel_fpu_begin(void) { struct task_struct *me = current; + this_cpu_write(in_kernel_fpu, true); + if (__thread_has_fpu(me)) { __thread_clear_has_fpu(me); __save_init_fpu(me); @@ -99,6 +106,8 @@ void __kernel_fpu_end(void) } else { stts(); } + + this_cpu_write(in_kernel_fpu, false); } EXPORT_SYMBOL(__kernel_fpu_end); -- 2.20.1