From 5187b28ff08249ab8a162e802209ed04e271ca02 Mon Sep 17 00:00:00 2001 From: Pekka Riikonen Date: Mon, 13 May 2013 14:32:07 +0200 Subject: x86: Allow FPU to be used at interrupt time even with eagerfpu With the addition of eagerfpu the irq_fpu_usable() now returns false negatives especially in the case of ksoftirqd and interrupted idle task, two common cases for FPU use for example in networking/crypto. With eagerfpu=off FPU use is possible in those contexts. This is because of the eagerfpu check in interrupted_kernel_fpu_idle(): ... * For now, with eagerfpu we will return interrupted kernel FPU * state as not-idle. TBD: Ideally we can change the return value * to something like __thread_has_fpu(current). But we need to * be careful of doing __thread_clear_has_fpu() before saving * the FPU etc for supporting nested uses etc. For now, take * the simple route! ... if (use_eager_fpu()) return 0; As eagerfpu is automatically "on" on those CPUs that also have the features like AES-NI this patch changes the eagerfpu check to return 1 in case the kernel_fpu_begin() has not been said yet. Once it has been the __thread_has_fpu() will start returning 0. Notice that with eagerfpu the __thread_has_fpu is always true initially. FPU use is thus always possible no matter what task is under us, unless the state has already been saved with kernel_fpu_begin(). [ hpa: this is a performance regression, not a correctness regression, but since it can be quite serious on CPUs which need encryption at interrupt time I am marking this for urgent/stable. ] Signed-off-by: Pekka Riikonen Link: http://lkml.kernel.org/r/alpine.GSO.2.00.1305131356320.18@git.silcnet.org Cc: v3.7+ Signed-off-by: H. Peter Anvin --- arch/x86/kernel/i387.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 245a71db401a..cb339097b9ea 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -22,23 +22,19 @@ /* * Were we in an interrupt that interrupted kernel mode? * - * For now, with eagerfpu we will return interrupted kernel FPU - * state as not-idle. TBD: Ideally we can change the return value - * to something like __thread_has_fpu(current). But we need to - * be careful of doing __thread_clear_has_fpu() before saving - * the FPU etc for supporting nested uses etc. For now, take - * the simple route! - * * On others, we can do a kernel_fpu_begin/end() pair *ONLY* if that * pair does nothing at all: the thread must not have fpu (so * that we don't try to save the FPU state), and TS must * be set (so that the clts/stts pair does nothing that is * visible in the interrupted kernel thread). + * + * Except for the eagerfpu case when we return 1 unless we've already + * been eager and saved the state in kernel_fpu_begin(). */ static inline bool interrupted_kernel_fpu_idle(void) { if (use_eager_fpu()) - return 0; + return __thread_has_fpu(current); return !__thread_has_fpu(current) && (read_cr0() & X86_CR0_TS); @@ -78,8 +74,8 @@ void __kernel_fpu_begin(void) struct task_struct *me = current; if (__thread_has_fpu(me)) { - __save_init_fpu(me); __thread_clear_has_fpu(me); + __save_init_fpu(me); /* We do 'stts()' in __kernel_fpu_end() */ } else if (!use_eager_fpu()) { this_cpu_write(fpu_owner_task, NULL); -- cgit v1.2.3