From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752765AbbAXLOn (ORCPT ); Sat, 24 Jan 2015 06:14:43 -0500 Received: from mail.skyhub.de ([78.46.96.112]:39502 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751557AbbAXLOi (ORCPT ); Sat, 24 Jan 2015 06:14:38 -0500 Date: Sat, 24 Jan 2015 12:14:30 +0100 From: Borislav Petkov To: "H. Peter Anvin" Cc: Ross Zwisler , linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH v2 0/2] add support for new persistent memory instructions Message-ID: <20150124111430.GA10084@pd.tnic> References: <1422045628-16225-1-git-send-email-ross.zwisler@linux.intel.com> <54C2D34D.7010709@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <54C2D34D.7010709@intel.com> 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 On Fri, Jan 23, 2015 at 03:03:41PM -0800, H. Peter Anvin wrote: > For the specific case of CLWB, we can use an "m" input rather than a > "+m" output, simply because CLWB (or CLFLUSH* used as a standin for CLWB > doesn't need to be ordered with respect to loads (whereas CLFLUSH* do). Well, we could do something like: volatile struct { char x[64]; } *p = __p; if (static_cpu_has(X86_FEATURE_CLWB)) asm volatile(".byte 0x66,0x0f,0xae,0x30" :: "m" (*p), "a" (p)); else asm volatile(ALTERNATIVE( ".byte 0x3e; clflush (%[pax])", ".byte 0x66; clflush (%[pax])", /* clflushopt (%%rax) */ X86_FEATURE_CLFLUSHOPT) : [p] "+m" (*p) : [pax] "a" (p)); which would simplify the alternative macro too. Generated asm looks ok to me (my objdump doesn't know CLWB yet :)): 0000000000000aa0 : aa0: 55 push %rbp aa1: 48 89 e5 mov %rsp,%rbp aa4: eb 0a jmp ab0 aa6: 48 89 f8 mov %rdi,%rax aa9: 66 0f ae 30 data16 xsaveopt (%rax) aad: 5d pop %rbp aae: c3 retq aaf: 90 nop ab0: 48 89 f8 mov %rdi,%rax ab3: 3e 0f ae 38 clflush %ds:(%rax) ab7: 5d pop %rbp ab8: c3 retq > Should we use an SFENCE as a standin if pcommit is unavailable, in case > we end up using CLFLUSHOPT? Btw, is PCOMMIT a lightweight SFENCE for this persistent memory aspect to make sure stuff has become persistent after executing it? But not all stuff like SFENCE so SFENCE is the bigger hammer? -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --