From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6BC00C10F14 for ; Mon, 8 Apr 2019 17:06:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2599821473 for ; Mon, 8 Apr 2019 17:06:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729180AbfDHRGD (ORCPT ); Mon, 8 Apr 2019 13:06:03 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:53469 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729151AbfDHRGC (ORCPT ); Mon, 8 Apr 2019 13:06:02 -0400 Received: from p5492ee6e.dip0.t-ipconnect.de ([84.146.238.110] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hDXiW-0003bn-Sm; Mon, 08 Apr 2019 19:05:57 +0200 Date: Mon, 8 Apr 2019 19:05:56 +0200 (CEST) From: Thomas Gleixner To: Sebastian Andrzej Siewior cc: linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Paolo Bonzini , =?ISO-8859-2?Q?Radim_Kr=E8m=E1=F8?= , kvm@vger.kernel.org, "Jason A. Donenfeld" , Rik van Riel , Dave Hansen Subject: Re: [PATCH 24/27] x86/fpu: Add a fastpath to __fpu__restore_sig() In-Reply-To: <20190403164156.19645-25-bigeasy@linutronix.de> Message-ID: References: <20190403164156.19645-1-bigeasy@linutronix.de> <20190403164156.19645-25-bigeasy@linutronix.de> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 3 Apr 2019, Sebastian Andrzej Siewior wrote: > The previous commits refactor the restoration of the FPU registers so > that they can be loaded from in-kernel memory. This overhead can be > avoided if the load can be performed without a pagefault. > > Attempt to restore FPU registers by invoking > copy_user_to_fpregs_zeroing(). If it fails try the slowpath which can handle > pagefaults. > > Signed-off-by: Sebastian Andrzej Siewior > --- > arch/x86/kernel/fpu/signal.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c > index a5b086ec426a5..f20e1d1fffa29 100644 > --- a/arch/x86/kernel/fpu/signal.c > +++ b/arch/x86/kernel/fpu/signal.c > @@ -242,10 +242,10 @@ sanitize_restored_xstate(union fpregs_state *state, > /* > * Restore the extended state if present. Otherwise, restore the FP/SSE state. > */ > -static inline int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only) > +static int copy_user_to_fpregs_zeroing(void __user *buf, u64 xbv, int fx_only) > { > if (use_xsave()) { > - if ((unsigned long)buf % 64 || fx_only) { > + if (fx_only) { This change is weird and not mentioned in the changelog.... > u64 init_bv = xfeatures_mask & ~XFEATURE_MASK_FPSSE; > copy_kernel_to_xregs(&init_fpstate.xsave, init_bv); > return copy_user_to_fxregs(buf); > @@ -327,7 +327,19 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size) > if (ret) > goto err_out; > envp = &env; > + } else { > + fpregs_lock(); > + pagefault_disable(); > + ret = copy_user_to_fpregs_zeroing(buf_fx, xfeatures, fx_only); > + pagefault_enable(); > + if (!ret) { > + fpregs_mark_activate(); > + fpregs_unlock(); > + return 0; > + } > + fpregs_unlock(); > } > + > if (use_xsave() && !fx_only) { > u64 init_bv = xfeatures_mask & ~xfeatures; > > -- > 2.20.1 > >