From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f45.google.com (mail-ej1-f45.google.com [209.85.218.45]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 876F614E2D4 for ; Thu, 11 Apr 2024 13:39:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712842782; cv=none; b=TVedcE7jEpHxHwctXf1Sv/YdvQ+FbpCrZC67uNzZ1h/MtPTelec+DlDZNN9K6EuIjyepTsuVblcABaITebJTJ5sU+76t+CUZVwel6r8yEbQILSwH/aaR1ZP1KtUK/KGoh6/csxZeMKFxkHg0nAzX6hdt88Cvw2KmxPHPSCSeglE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712842782; c=relaxed/simple; bh=Q4lqBLJ/e15bzi65GJXnnE58jRGWZqvbLdUwj7++o/U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ats03DSsUOrUPUpRGUoenoyHjb5EdEVE00mV3HPMj55gqPiVKZyQr695CodXLxXHoRxB9BwnFU9laN9LeYtVzyEPWIWfUbXSzhsIUmzeii89251ZS1hMezl2L0f5FbLJz6jeD+6tPM43NFzViHoeGQXW17CcoZVH4VtGEPkzz+8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=bWsAx8hE; arc=none smtp.client-ip=209.85.218.45 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="bWsAx8hE" Received: by mail-ej1-f45.google.com with SMTP id a640c23a62f3a-a46a7208eedso1121340566b.0 for ; Thu, 11 Apr 2024 06:39:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1712842777; x=1713447577; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=Nw5oWo8SbG/JjbLUd+pDYICRWpYvqotAi1XzjeWc850=; b=bWsAx8hEMGpeM1lyQr0o//O4d3QluxZexMku39HXmCJiNaikY+UukL7dtx2nt+e/5r r/um/s/W8Ekxq+nOXIlL0UW2pgNxJiiRciz/iQqbXfMSTUPonM8TYzTfPWR+MR2r+4Hu gnNMrEjK4juKqdD8PPPJrH/mrCz4WQwjfuPXs64O1PtpQaxbjfCzt9BIOHliaB4L9qL4 dr7e+EwD7gj/Qr3DQG/qAL1gp803UcmqRSdU/PMC1Ev/T0O56I0wu1ED+ACdxr6ehSHZ cygw/3K30ERwvhpqVvon4xX+b870RThzZZSI6ThBdchHp/E0hR31FJQITj9tM2pGZ4o+ Fd9Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1712842777; x=1713447577; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=Nw5oWo8SbG/JjbLUd+pDYICRWpYvqotAi1XzjeWc850=; b=vVMTotlSq34r8g474NWdqfcgomcijjS+kiRCjdMVlMkFVOuUocooNGSvezRWygh6IO /RMwR5QuewLbWT7aOfIaq6RScqj6rnuByiXFfI3wJVFFrHDXRRvZiOz9mWMZdpa+ou9Z fxKretHOpeAec9nBjwf2/BebAPhogTrziUKyrjwumem8o2qsMXzbIEM8vv2Id+RkCYJf R69IQqz76jvt0bqYzKse6Q+MLeJQtFGL8bW/OChs0pym0wc/3v0A3fdd3VLun7T2Oz1j C7cpodGniGjMk1tjvr5U62NSadHO2M3W7+vXcoKEacuU6CJR2wFRR3o7vTk1IQG4HnJO bpzQ== X-Forwarded-Encrypted: i=1; AJvYcCWXN0KzCdjm81H4XfAxNkMq8oP7uQgeTSHNJR4jBPqVE/L3OisJLWlpWUPqkjjDOl9RBCT2bu85rlia6258uSsJw+Oe0ndAT7qw8+s/ X-Gm-Message-State: AOJu0Yyy2Is7EqHinvhb29YdZvGFzfo2Bwf27eLEEGpdb+/w5oPVpVVL 0FT0wIki/CGDyZn/c04FRaEFnQ+wxTlcSpcxLbrgLVSkJkLhcFG5gTJVLZe5WTI= X-Google-Smtp-Source: AGHT+IFDZdEXgvpYFvYDPlTbFe/I24LhPGaam33E+x0qZmk8Ha0VpCJchtO79TGC7Q5GKUPegeSFeg== X-Received: by 2002:a17:907:ea5:b0:a51:c281:60f3 with SMTP id ho37-20020a1709070ea500b00a51c28160f3mr4251234ejc.77.1712842776616; Thu, 11 Apr 2024 06:39:36 -0700 (PDT) Received: from ?IPV6:2003:e5:8705:9b00:4df1:9dd5:4f97:24a? (p200300e587059b004df19dd54f97024a.dip0.t-ipconnect.de. [2003:e5:8705:9b00:4df1:9dd5:4f97:24a]) by smtp.gmail.com with ESMTPSA id r10-20020a1709060d4a00b00a46a9cdcfa5sm759701ejh.162.2024.04.11.06.39.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Apr 2024 06:39:36 -0700 (PDT) Message-ID: <99c720a9-b042-46d3-8182-cb9bcabb89db@suse.com> Date: Thu, 11 Apr 2024 15:39:35 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] locking/x86/xen: Use try_cmpxchg() in xen_alloc_p2m_entry() Content-Language: en-US To: Uros Bizjak , xen-devel@lists.xenproject.org, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" References: <20240405083335.507471-1-ubizjak@gmail.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= In-Reply-To: <20240405083335.507471-1-ubizjak@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 05.04.24 10:32, Uros Bizjak wrote: > Use try_cmpxchg() instead of cmpxchg(*ptr, old, new) == old. > > The x86 CMPXCHG instruction returns success in the ZF flag, > so this change saves a compare after CMPXCHG. > > Also, try_cmpxchg() implicitly assigns old *ptr value to "old" > when CMPXCHG fails. There is no need to explicitly assign > old *ptr value to the temporary, which can simplify the > surrounding source code. > > No functional change intended. > > Signed-off-by: Uros Bizjak > Cc: Juergen Gross > Cc: Boris Ostrovsky > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: Dave Hansen > Cc: "H. Peter Anvin" Reviewed-by: Juergen Gross Juergen