From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752677AbbASSxW (ORCPT ); Mon, 19 Jan 2015 13:53:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42451 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751922AbbASSxU (ORCPT ); Mon, 19 Jan 2015 13:53:20 -0500 Date: Mon, 19 Jan 2015 19:52:12 +0100 From: Oleg Nesterov To: Rik van Riel , Linus Torvalds , Suresh Siddha Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, matt.fleming@intel.com, bp@suse.de, pbonzini@redhat.com, tglx@linutronix.de, luto@amacapital.net Subject: [PATCH 3/3] x86, fpu: don't abuse FPU in kernel threads if use_eager_fpu() Message-ID: <20150119185212.GD16427@redhat.com> References: <1421012793-30106-1-git-send-email-riel@redhat.com> <20150115191918.GA27332@redhat.com> <20150119185109.GA16427@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150119185109.GA16427@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Afaics there is no reason why kernel threads should have FPU context even if use_eager_fpu() == T. Now that interrupted_kernel_fpu_idle() does not check __thread_has_fpu() we can remove the init_fpu() code from eager_fpu_init() and change flush_thread() called by do_execve() to initialize FPU. Note: of course, the change in flush_thread() is horrible and must be cleanuped. We need the new helper, and flush_thread() should return the error if init_fpu() fails. Signed-off-by: Oleg Nesterov --- arch/x86/kernel/process.c | 7 +++++++ arch/x86/kernel/xsave.c | 13 +------------ 2 files changed, 8 insertions(+), 12 deletions(-) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index e127dda..dd9a069 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -130,6 +130,7 @@ void flush_thread(void) flush_ptrace_hw_breakpoint(tsk); memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array)); + drop_init_fpu(tsk); /* * Free the FPU state for non xsave platforms. They get reallocated @@ -137,6 +138,12 @@ void flush_thread(void) */ if (!use_eager_fpu()) free_thread_xstate(tsk); + else if (!used_math()) { + /* kthread execs. TODO: cleanup this horror. */ + if (WARN_ON(init_fpu(current))) + force_sig(SIGKILL, current); + math_state_restore(); + } } static void hard_disable_TSC(void) diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c index 0de1fae..de9dcf8 100644 --- a/arch/x86/kernel/xsave.c +++ b/arch/x86/kernel/xsave.c @@ -688,7 +688,7 @@ void eager_fpu_init(void) { static __refdata void (*boot_func)(void) = eager_fpu_init_bp; - clear_used_math(); + WARN_ON(used_math()); current_thread_info()->status = 0; if (eagerfpu == ENABLE) @@ -703,17 +703,6 @@ void eager_fpu_init(void) boot_func(); boot_func = NULL; } - - /* - * This is same as math_state_restore(). But use_xsave() is - * not yet patched to use math_state_restore(). - */ - init_fpu(current); - __thread_fpu_begin(current); - if (cpu_has_xsave) - xrstor_state(init_xstate_buf, -1); - else - fxrstor_checking(&init_xstate_buf->i387); } /* -- 1.5.5.1