Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757227AbbBFQGV (ORCPT ); Fri, 6 Feb 2015 11:06:21 -0500 Received: from mail.skyhub.de ([78.46.96.112]:48974 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756625AbbBFQGS (ORCPT ); Fri, 6 Feb 2015 11:06:18 -0500 Date: Fri, 6 Feb 2015 17:05:47 +0100 From: Borislav Petkov To: Scotty Bauer Cc: tglx@linutronix.de, mingo@redheat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH] x86/smpboot: check if CLFLUSH is actually necessary Message-ID: <20150206160547.GF3220@pd.tnic> References: <54CBF6F9.5040508@eng.utah.edu> <20150130233142.GA1884@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150130233142.GA1884@pd.tnic> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2429 Lines: 78 On Sat, Jan 31, 2015 at 12:31:42AM +0100, Borislav Petkov wrote: > asm volatile(ALTERNATIVE(ASM_NOP3, "clflush %[p]", X86_BUG_CLFLUSH_MONITOR) > : [p] "+m" (*mwait_ptr)); > > Totally untested though - it is supposed to show the idea only. Yeah, here's a working diff, ontop of this patchset: https://lkml.kernel.org/r/1422987390-17878-1-git-send-email-bp@alien8.de --- diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 6d7022c683e3..771ebd6e8b77 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1432,7 +1432,11 @@ static inline void mwait_play_dead(void) * case where we return around the loop. */ mb(); - clflush(mwait_ptr); + + asm volatile(ALTERNATIVE("", "clflush %[p]", + X86_BUG_CLFLUSH_MONITOR) + : [p] "+m" (*(unsigned long *)mwait_ptr)); + mb(); __monitor(mwait_ptr, 0, 0); mb(); -- At build time you have: -- ... ffffffff81038dcc: 65 48 8b 1c 25 88 ab mov %gs:0xab88,%rbx # movq %gs:kernel_stack,%rbx #, pfo_ret__ ffffffff81038dd3: 00 00 ffffffff81038dd5: 48 81 eb c8 3f 00 00 sub $0x3fc8,%rbx # subq $16328, %rbx #, mwait_ptr ffffffff81038ddc: 0f 09 wbinvd ffffffff81038dde: 45 31 e4 xor %r12d,%r12d ffffffff81038de1: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) ffffffff81038de8: 0f ae f0 mfence ffffffff81038deb: 90 nop ffffffff81038dec: 90 nop ffffffff81038ded: 90 nop ffffffff81038dee: 0f ae f0 mfence ffffffff81038df1: 48 89 d8 mov %rbx,%rax ... -- which during runtime, on those affected machines only, gets patched to: --- ... ffffffff81038dcc: mov %gs:0xab88,%rbx ffffffff81038dd5: sub $0x3fc8,%rbx ffffffff81038ddc: wbinvd ffffffff81038dde: xor %r12d,%r12d ffffffff81038de1: nopl 0x0(%rax) ffffffff81038de8: mfence ffffffff81038deb: clflush (%rbx) <--- ffffffff81038dee: mfence ffffffff81038df1: mov %rbx,%rax ... --- :-) -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/