From nobody Mon Sep 15 01:52:28 2025 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 49205C67871 for ; Mon, 16 Jan 2023 16:47:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233648AbjAPQra (ORCPT ); Mon, 16 Jan 2023 11:47:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233714AbjAPQq7 (ORCPT ); Mon, 16 Jan 2023 11:46:59 -0500 Received: from mail-ej1-x635.google.com (mail-ej1-x635.google.com [IPv6:2a00:1450:4864:20::635]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA7C13B0D1 for ; Mon, 16 Jan 2023 08:34:51 -0800 (PST) Received: by mail-ej1-x635.google.com with SMTP id vw16so6211454ejc.12 for ; Mon, 16 Jan 2023 08:34:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=VKurv2fBxvZBgI8zffGgWfWcbuA/mY2GbURj2GBqtuI=; b=hDKG6BvYivh2vxmy8FbZagCDJ7pdkQqIBjP64nFrRQh2tXrf5j9lICcPG+Wn2DhvDs t7Rq/pK8Hf0N7V7VMT/y6cafH5BMy6f3ELyJiSvoG65kL3Gwer7GHV2csDkcM2GA3BC5 aGhw1UdkswTFWrivsMwTB0groXZpxAtVvr41NDXjVSoog0GCclTTWqySKKjmLmdHZm32 FuExRep2B67j11jv2eApvVYEovtnufCcXgOrMvb58oiXZLPxUwTX8qySUiIVaybH9D/k b4jvPRzWcv+w3ipU0Vv6GP3m+sGsksg610ijpcvdVajkLB3vsfhpDpLDt3j3yQ5Kdjx5 YLhg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=VKurv2fBxvZBgI8zffGgWfWcbuA/mY2GbURj2GBqtuI=; b=TfyTsg+sBCyrUg0MjSNGPxo8Nyr4fJtVIl0Htc3c2Zib8iUhkgHIHXsrNsIBgr+C9i T5hInhyz/kTFPvFQLx6CR0owVeiRDHh9LH2G2Fncv62DEezUh5JO91g0E8VcXJAphloX 6/Fi1rlpGld37491R1lmFJNCygsClnneblgOWKxumCXiAE6kaTayDRDuD+z4lMR77KOe pZllKHob5R4cd0eZFI/D6lBxl/i9/kJk40cVrx9156I3JGZr2YeTq5J40w+1QxEngaxh FipysGLVGDXzslK1T3z8OJfhcIbMXWjWujdIBrq81OpDyLray1O8bnDy78xpxEuX61aA Oziw== X-Gm-Message-State: AFqh2kpuXa+PbfdrFDGRqmUu1oZKwq3uprJLq/PL8+hSLvLR7/Ua2fi5 hZOe5r3QSC7fg0VgvN6T6mg= X-Google-Smtp-Source: AMrXdXtwBz3Uu0Cw7081MlKCKmhbz7gEc4fI3TqKyRF/mOPKqlazXXsAB1bNvFtKi7Yz7UnCzsqkTg== X-Received: by 2002:a17:906:1681:b0:86e:c9e2:6313 with SMTP id s1-20020a170906168100b0086ec9e26313mr6806079ejd.32.1673886890330; Mon, 16 Jan 2023 08:34:50 -0800 (PST) Received: from fedora.. ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id kx5-20020a170907774500b007c14ae38a80sm11887805ejc.122.2023.01.16.08.34.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Jan 2023 08:34:49 -0800 (PST) From: Uros Bizjak To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" Subject: [PATCH] x86/PAT: use try_cmpxchg in set_page_memtype Date: Mon, 16 Jan 2023 17:34:46 +0100 Message-Id: <20230116163446.4734-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Use try_cmpxchg instead of cmpxchg (*ptr, old, new) =3D=3D old in set_page_memtype. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. Note that the value from *ptr should be read using READ_ONCE to prevent the compiler from merging, refetching or reordering the read. No functional change intended. Signed-off-by: Uros Bizjak Cc: Dave Hansen Cc: Andy Lutomirski Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: "H. Peter Anvin" --- arch/x86/mm/pat/memtype.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index fb4b1b5e0dea..6d1ba2dda35d 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -159,10 +159,10 @@ static inline void set_page_memtype(struct page *pg, break; } =20 + old_flags =3D READ_ONCE(pg->flags); do { - old_flags =3D pg->flags; new_flags =3D (old_flags & _PGMT_CLEAR_MASK) | memtype_flags; - } while (cmpxchg(&pg->flags, old_flags, new_flags) !=3D old_flags); + } while (!try_cmpxchg(&pg->flags, &old_flags, new_flags)); } #else static inline enum page_cache_mode get_page_memtype(struct page *pg) --=20 2.39.0