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 A629E1E5713 for ; Thu, 15 May 2025 07:33:13 +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=1747294395; cv=none; b=ePXHiISIx4ZK9rpgQ9PwQpKOeu6oUyeuPQtbPSXExAOBsqlWfAABnnQFfIXq+oFZSmIBGQmT/MDLlGVtQIcsL4S1gwXTTOr49RWI1HriGhfdIqymEchH9PupelUQnME/G+jOxMqxWZ6IGE9pVbgohKNuS4GbU8NNf9cR7DiBSu8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747294395; c=relaxed/simple; bh=JNzgfSL4CsTGy1bjrPz4RxndSl0WA53cyHjzmh8RFj4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jl5dlnMWnOrGX3SF8rphUimbMdKh22Esvk7xnTVPtCx2gxG7q8EnhLViwXTNaVfWtKEwoRTgbolTe6l5wrDB++9wfBh6DtqmsdudKlI9j9CSnMgXFHI5DKJjywSMG7RW8t0zM6c2pjHQa3rVxsXYXFOWFG65tg0QbriHj46O2RU= 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=OeZftPa4; 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="OeZftPa4" 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 54F7WfsF3336298 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Thu, 15 May 2025 00:32:41 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 54F7WfsF3336298 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025042001; t=1747294363; bh=FTKlSsiJd9+jpos7AVLXF8LAqgwtfl1Qy7H7vRzCDXE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OeZftPa4P2RcLNrfq7mYvwL9TgxRMcLlkVGZC6h8vETFbJVCjpBbzmpzH5AR13wKx 15mv9dkcpvv5ouP63h6d4FyAbbBv4ahXZZT/mJEs0YcVe4dSsuiidCYyb5eLIFmmab KZh7WExvvM7f5dcUXiiH4kI087BVfYMnwIxDBqPfWZBau2sgqY1q7vFYn0CwCYjxM9 k2IdZTAsWYVBOheuyRj88cuKgPcjoyTQbvMyOTslRINSkfMVXRDIiVGVCAqieKjmOF vIstWyCK+xY4GqiDXwaoMJ8FcLhCdyf9Y7Wv9kaBeH/qOTfV0h+xsRne4kDWAibHx3 4HrOazqt1wu0g== Message-ID: <652dfd63-e41c-4d7a-8fea-40509e8191ef@zytor.com> Date: Thu, 15 May 2025 00:32:40 -0700 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/6] x86/paravirt: Switch MSR access pv_ops functions to instruction interfaces To: "H. Peter Anvin" , =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, Peter Zijlstra Cc: Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Boris Ostrovsky , xen-devel@lists.xenproject.org References: <20250506092015.1849-1-jgross@suse.com> <20250506092015.1849-6-jgross@suse.com> <722f5b30-20e9-4540-98e4-d211d7c44cbe@zytor.com> <9f4e33d5-9cb3-4079-b764-87a15265fd52@suse.com> <6cc20ef6-d8e5-4c74-89d9-6a949c84b397@suse.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/13/2025 3:24 PM, H. Peter Anvin wrote: > On May 12, 2025 11:06:02 PM PDT, "Jürgen Groß" wrote: >> On 13.05.25 07:55, Xin Li wrote: >>> On 5/12/2025 4:24 AM, Juergen Gross wrote: >>>> Now with the mentioned patch really attached. :-) >>>> >>> >>> Does it allow patching with an instruction more than 6 bytes long? >>> >>> The immediate form MSR instructions are 9 bytes long. >> >> Yes, shouldn't be a problem. >> >> >> Juergen > > However, it is more than that. The immediate instructions have a different interface, and it makes more sense to use the extra bytes to shuffle the bits around for the legacy forms: > > Write: > > mov %rax,%rdx > shr $32,%rdx > wrmsr(ns) > > Read: > > rdmsr > shl $32,%rdx > or %rdx,%rax > > For the write case, this also means that two separate trap points are needed. > > As far as Xen (the only user of pv msrs), note that it only paravirtualizes a very small number of MSRs, and some of those are fairly performance sensitive, so not going through the Xen framework for MSRs known to be either native or null on Xen would definitely be a win. > > Hi Juergen, I have some update on this thread while working on it. If we continue down the path of maintaining pvops MSR APIs as this patch series does, it seems we’ll need to duplicate the ALTERNATIVE code in three different places. 1) The MSR access primitives defined in , which is used when CONFIG_PARAVIRT=n. 2) The pvops native MSR functions pv_native_{rd,wr}msr{,_safe}() defined in arch/x86/kernel/paravirt.c, used when CONFIG_PARAVIRT=y on bare metal. 3) The pvops Xen MSR functions paravirt_{read,write}_msr{,_safe}() defined in , used when CONFIG_PARAVIRT_XXL=y. hpa had mentioned to me earlier that this would be a maintenance burden — something I only truly realized once I got hands-on with it. Maybe you have something in mind to address it? Also add PeterZ to the To list because he cares it. Thanks! Xin