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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E85BBC433F5 for ; Mon, 16 May 2022 14:04:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244144AbiEPOEW (ORCPT ); Mon, 16 May 2022 10:04:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232054AbiEPOEO (ORCPT ); Mon, 16 May 2022 10:04:14 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6C55E3915C for ; Mon, 16 May 2022 07:04:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652709852; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=msH0fbWMB2FjlFoGW4LyhQTRlos1WPFFFL4WveZKmPQ=; b=aYXlTqPGIpl234AUF1g65d6s6Pugpk5Gbpooh+QCp9EsB+gXNFEzrE3OKM8emI8797/oEJ 1D4FkyPAGuQVDqBhvQQeBCgblNk0l9NoUqWTF28ZcqnSWEecj2nQVLAQjdOJTjlc1qpWVX pXiREfQV+75u3fZxKS2VPfBQSTQR01M= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-558-HFWdWCckNxiAyEOTdL7HQw-1; Mon, 16 May 2022 10:04:09 -0400 X-MC-Unique: HFWdWCckNxiAyEOTdL7HQw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4037D89B841; Mon, 16 May 2022 14:04:08 +0000 (UTC) Received: from starship (unknown [10.40.192.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id CC86D2026D64; Mon, 16 May 2022 14:04:04 +0000 (UTC) Message-ID: Subject: Re: [PATCH] locking/atomic/x86: Introduce try_cmpxchg64 From: Maxim Levitsky To: Uros Bizjak , Sean Christopherson Cc: Peter Zijlstra , X86 ML , LKML , kvm@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Will Deacon , Boqun Feng , Mark Rutland , "Paul E. McKenney" , Marco Elver Date: Mon, 16 May 2022 17:04:03 +0300 In-Reply-To: References: <20220510154217.5216-1-ubizjak@gmail.com> <20220510165506.GP76023@worktop.programming.kicks-ass.net> <20220511075409.GX76023@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2022-05-11 at 21:54 +0200, Uros Bizjak wrote: > On Wed, May 11, 2022 at 6:04 PM Sean Christopherson wrote: > > On Wed, May 11, 2022, Uros Bizjak wrote: > > > On Wed, May 11, 2022 at 9:54 AM Peter Zijlstra wrote: > > > > Still, does 32bit actually support that stuff? > > > > > > Unfortunately, it does: > > > > > > kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \ > > > vmx/evmcs.o vmx/nested.o vmx/posted_intr.o > > > > > > And when existing cmpxchg64 is substituted with cmpxchg, the > > > compilation dies for 32bits with: > > > > ... > > > > > > Anyway, your patch looks about right, but I find it *really* hard to > > > > care about 32bit code these days. > > > > > > Thanks, this is also my sentiment, but I hope the patch will enable > > > better code and perhaps ease similar situation I have had elsewhere. > > > > IMO, if we merge this it should be solely on the benefits to 64-bit code. Yes, > > KVM still supports 32-bit kernels, but I'm fairly certain the only people that > > run 32-bit KVM are KVM developers. 32-bit KVM has been completely broken for > > multiple releases at least once, maybe twice, and no one ever complained. > > Yes, the idea was to improve cmpxchg64 with the implementation of > try_cmpxchg64 for 64bit targets. However, the issue with 32bit targets > stood in the way, so the effort with 32-bit implementation was mainly > to unblock progression for 64-bit targets. Would that allow tdp mmu to work on 32 bit? Best regards, Maxim Levitsky > > Uros. >