From patchwork Fri Nov 26 00:31:08 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej S. Szmigiero" X-Patchwork-Id: 12640005 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 13037C433F5 for ; Fri, 26 Nov 2021 00:33:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352047AbhKZAgr (ORCPT ); Thu, 25 Nov 2021 19:36:47 -0500 Received: from vps-vb.mhejs.net ([37.28.154.113]:55292 "EHLO vps-vb.mhejs.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239062AbhKZAep (ORCPT ); Thu, 25 Nov 2021 19:34:45 -0500 Received: from MUA by vps-vb.mhejs.net with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mqP9B-0007H6-VT; Fri, 26 Nov 2021 01:31:26 +0100 From: "Maciej S. Szmigiero" To: Paolo Bonzini Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Igor Mammedov , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/3] KVM: Use atomic_long_cmpxchg() instead of an open-coded variant Date: Fri, 26 Nov 2021 01:31:08 +0100 Message-Id: <7bdc7ee3dcc09a109cfaf9fb8662fb49ca0bec2c.1637884349.git.maciej.szmigiero@oracle.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: "Maciej S. Szmigiero" Open-coding a cmpxchg()-like operation is significantly less readable than a direct call. Also, the open-coded version compiles to multiple instructions with a branch on x86, instead of just a single instruction. Since technically the open-coded variant didn't guarantee actual atomicity add a comment there, too, that this property isn't strictly required in this case. Signed-off-by: Maciej S. Szmigiero --- virt/kvm/kvm_main.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index d4399db06d49..367c1cba26d2 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1378,8 +1378,12 @@ static void kvm_replace_memslot(struct kvm *kvm, hash_del(&old->id_node[idx]); interval_tree_remove(&old->hva_node[idx], &slots->hva_tree); - if ((long)old == atomic_long_read(&slots->last_used_slot)) - atomic_long_set(&slots->last_used_slot, (long)new); + /* + * The atomicity isn't strictly required here since we are + * operating on an inactive memslots set anyway. + */ + atomic_long_cmpxchg(&slots->last_used_slot, + (unsigned long)old, (unsigned long)new); if (!new) { kvm_erase_gfn_node(slots, old);