From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2682B27468 for ; Thu, 10 Apr 2025 03:18:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744255129; cv=none; b=N2p/Cm7fK3t56oayDyGLzEtOjP7jh84+JY/zn3t2D7UjGPJw3EK0HE4wVAzQyUkshv39iGoPAjxubOtND1+Lh9ZhSXTMpieFYzyrPPxsGowtsGHeSnHsYOo1S3hfXtBqt/5+Tzf8o6zvvxIdD/iEtxee13JEe4II/9LBT5HQMMA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744255129; c=relaxed/simple; bh=En3M8+sPUg3r5CpIH4rbVUPLsPjMTgBNlUfmIZpf1u4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HNErg6YXJ4UE5Y2ssc+sKvcKkxG5z4OogUxlOERrL070h99RYq9nxmlwx73SeP8lB9RBXX0dGQys1WKcH5p25Tn5myOw52c+48/T8RWrAp5v/LK0R1qNiC9gobBCda03VMjKoIRxz6jCIl3gjB+/W+6Fkc1Mym5OZRXqZ/IlDoo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=WysfUYTw; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="WysfUYTw" Received: from [192.168.7.202] ([71.202.166.45]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 53A3IC7R3875792 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Wed, 9 Apr 2025 20:18:13 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 53A3IC7R3875792 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025032001; t=1744255094; bh=WQvzgiSKQjwsQO/1UyRD7P7gh1UdDMANljygNiYHs1Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WysfUYTwKtmvkf4W1Dy9Re/Oi77kncY0buVC1NnifYo37GR2dpsM5Gg3St1A3Mtoy FGYmP34HNgiqkR23ns3bTjH/X3vQbMmKs/LSt9CBynnA+uIeq2Oo+4qz0DQg/L9CtW vIANl9X8sWMIbIL4kdM0UzXY27ZRwxF+4APfi66LzdnXGw4x0QcSWnJQilUTMPSIMz iz9/FAeEBPqsXwnBRr+MfjeieEs5C4/XTw9kmxla1ySN4NMX12oNycaO/FfXCGihwY bRRt5hpTuyInD43+vQEpCMBBpXvSitp/5yYb/g21kOQalL70XKBhNkm+5WPXkZp2kN ggk6DgJDncOOg== Message-ID: <63ab3ea9-c55d-48d2-8344-fb4314baf240@zytor.com> Date: Wed, 9 Apr 2025 20:18:12 -0700 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 06/20] x86/msr: Standardize on 'u32' MSR indices in To: "H. Peter Anvin" , Ingo Molnar , linux-kernel@vger.kernel.org Cc: Juergen Gross , Dave Hansen , Linus Torvalds , Peter Zijlstra , Borislav Petkov , Thomas Gleixner References: <20250409202907.3419480-1-mingo@kernel.org> <20250409202907.3419480-7-mingo@kernel.org> <9c014962-d4cb-4e68-be15-efbe2ea26531@zytor.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; keydata= xsDNBGUPz1cBDACS/9yOJGojBFPxFt0OfTWuMl0uSgpwk37uRrFPTTLw4BaxhlFL0bjs6q+0 2OfG34R+a0ZCuj5c9vggUMoOLdDyA7yPVAJU0OX6lqpg6z/kyQg3t4jvajG6aCgwSDx5Kzg5 Rj3AXl8k2wb0jdqRB4RvaOPFiHNGgXCs5Pkux/qr0laeFIpzMKMootGa4kfURgPhRzUaM1vy bsMsL8vpJtGUmitrSqe5dVNBH00whLtPFM7IbzKURPUOkRRiusFAsw0a1ztCgoFczq6VfAVu raTye0L/VXwZd+aGi401V2tLsAHxxckRi9p3mc0jExPc60joK+aZPy6amwSCy5kAJ/AboYtY VmKIGKx1yx8POy6m+1lZ8C0q9b8eJ8kWPAR78PgT37FQWKYS1uAroG2wLdK7FiIEpPhCD+zH wlslo2ETbdKjrLIPNehQCOWrT32k8vFNEMLP5G/mmjfNj5sEf3IOKgMTMVl9AFjsINLHcxEQ 6T8nGbX/n3msP6A36FDfdSEAEQEAAc0WWGluIExpIDx4aW5Aenl0b3IuY29tPsLBDQQTAQgA NxYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89XBQkFo5qAAhsDBAsJCAcFFQgJCgsFFgID AQAACgkQa70OVx2uN1HUpgv/cM2fsFCQodLArMTX5nt9yqAWgA5t1srri6EgS8W3F+3Kitge tYTBKu6j5BXuXaX3vyfCm+zajDJN77JHuYnpcKKr13VcZi1Swv6Jx1u0II8DOmoDYLb1Q2ZW v83W55fOWJ2g72x/UjVJBQ0sVjAngazU3ckc0TeNQlkcpSVGa/qBIHLfZraWtdrNAQT4A1fa sWGuJrChBFhtKbYXbUCu9AoYmmbQnsx2EWoJy3h7OjtfFapJbPZql+no5AJ3Mk9eE5oWyLH+ QWqtOeJM7kKvn/dBudokFSNhDUw06e7EoVPSJyUIMbYtUO7g2+Atu44G/EPP0yV0J4lRO6EA wYRXff7+I1jIWEHpj5EFVYO6SmBg7zF2illHEW31JAPtdDLDHYcZDfS41caEKOQIPsdzQkaQ oW2hchcjcMPAfyhhRzUpVHLPxLCetP8vrVhTvnaZUo0xaVYb3+wjP+D5j/3+hwblu2agPsaE vgVbZ8Fx3TUxUPCAdr/p73DGg57oHjgezsDNBGUPz1gBDAD4Mg7hMFRQqlzotcNSxatlAQNL MadLfUTFz8wUUa21LPLrHBkUwm8RujehJrzcVbPYwPXIO0uyL/F///CogMNx7Iwo6by43KOy g89wVFhyy237EY76j1lVfLzcMYmjBoTH95fJC/lVb5Whxil6KjSN/R/y3jfG1dPXfwAuZ/4N cMoOslWkfZKJeEut5aZTRepKKF54T5r49H9F7OFLyxrC/uI9UDttWqMxcWyCkHh0v1Di8176 jjYRNTrGEfYfGxSp+3jYL3PoNceIMkqM9haXjjGl0W1B4BidK1LVYBNov0rTEzyr0a1riUrp Qk+6z/LHxCM9lFFXnqH7KWeToTOPQebD2B/Ah5CZlft41i8L6LOF/LCuDBuYlu/fI2nuCc8d m4wwtkou1Y/kIwbEsE/6RQwRXUZhzO6llfoN96Fczr/RwvPIK5SVMixqWq4QGFAyK0m/1ap4 bhIRrdCLVQcgU4glo17vqfEaRcTW5SgX+pGs4KIPPBE5J/ABD6pBnUUAEQEAAcLA/AQYAQgA JhYhBIUq/WFSDTiOvUIqv2u9DlcdrjdRBQJlD89ZBQkFo5qAAhsMAAoJEGu9DlcdrjdR4C0L /RcjolEjoZW8VsyxWtXazQPnaRvzZ4vhmGOsCPr2BPtMlSwDzTlri8BBG1/3t/DNK4JLuwEj OAIE3fkkm+UG4Kjud6aNeraDI52DRVCSx6xff3bjmJsJJMb12mWglN6LjdF6K+PE+OTJUh2F dOhslN5C2kgl0dvUuevwMgQF3IljLmi/6APKYJHjkJpu1E6luZec/lRbetHuNFtbh3xgFIJx 2RpgVDP4xB3f8r0I+y6ua+p7fgOjDLyoFjubRGed0Be45JJQEn7A3CSb6Xu7NYobnxfkwAGZ Q81a2XtvNS7Aj6NWVoOQB5KbM4yosO5+Me1V1SkX2jlnn26JPEvbV3KRFcwV5RnDxm4OQTSk PYbAkjBbm+tuJ/Sm+5Yp5T/BnKz21FoCS8uvTiziHj2H7Cuekn6F8EYhegONm+RVg3vikOpn gao85i4HwQTK9/D1wgJIQkdwWXVMZ6q/OALaBp82vQ2U9sjTyFXgDjglgh00VRAHP7u1Rcu4 l75w1xInsg== In-Reply-To: <9c014962-d4cb-4e68-be15-efbe2ea26531@zytor.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/9/2025 6:37 PM, H. Peter Anvin wrote: > On 4/9/25 14:55, Xin Li wrote: >> >> It looks to me that we don't use the "const" qualifier in the code a >> lot.  However since the MSR index is usually not expected to change >> inside the MSR API implementations, would it be nicer to add the "const" >> qualifier? >> >> The same to the MSR value of MSR write APIs. >> > > "const" on an automatic variable (including function arguments) is > usually not very meaningful, unless it is manifest as a memory object > (see below.) > > Personally I tend to use "const" anyway in more complex functions to > make it clear that a variable is not expected to change while in scope > (and I also prefer to reduce the scope of a variable as much as > possible), but for a simple function like this it is more clutter than > anything else. Good point! A question NOT related to this patch set, the MSR write API prototype defined in struct pv_cpu_ops as: void (*write_msr)(unsigned int msr, unsigned low, unsigned high); Will it be better to add "const" to its arguments? I.e., void (*write_msr)(const u32 msr, const u32 low, const u32 high); > Now, "const" on a *memory object* (pointer target) is a very different > thing and should in general be used where ever writing to an object is > not going to happen. > > An automatic variable becomes manifest as a memory object if its address > is taken anywhere in its scope (using the & operator or an unindexed > array) and the address of that pointer stored. The last part means that > the compiler (if it is is smart enough) can take a sequence of > operations equivalent to *& and eliminate it. > > Keep in mind that, for C (not necessarily C++): > > 1. in *all* cases "foo[x]" is exactly equivalent to "*(foo + x)" > 2. *if* "foo" is declared as an array type, then "foo" is exactly > equivalent to "&foo[0]". > > "const" in C a little less strict than you would like; the only way in C > before C23 to declare a "true" constant is using enum or a #define macro > (which of course pollutes the global namespace). In block scope it > usually doesn't matter for scalar types and const or static const will > work just fine, but it is only in C23 than C imported "constexpr" from > C++ (which has had it since C++11.) Nice to know. Thanks! Xin