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 495AF1EFF80 for ; Fri, 13 Jun 2025 07:32:26 +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=1749799948; cv=none; b=XFzeZfZj2IiG7LzpR2Lc5f3vOMY93czliqLkbaygDKLbKJ+8Laf3+peYabTa71J6AKheaBdyvUli83ejjd/Z2u6eVaox3q4+nE2ANfg7Hd5GHRiphh7sKHk9sobDvJTdK6pmPndRB3SFRopxJ4dINvsTCa2zqvO7I0XTzen6xxE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749799948; c=relaxed/simple; bh=zck7WMGgzZa3cnxbw9rpUAXo+PXfsfoJCR4vIZekB7s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GaDXMAUnkaO33/cAQBJxBsQ4LuhYqCk/BYOuMrTyUB6H4qEWBp/CxBIuBm0Ta8FVKSPClMAIbNfBydG0nPvLf/afKPES+1xM6W8Bs/xwcI80zg7juvDNDvTxLiuNgEv3maGVt+1oNfJ8dZ5NmDECsOCtscWPxdaK0ipIaKBtd1A= 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=ssHkh09E; 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="ssHkh09E" 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 55D7VjwM3704239 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Fri, 13 Jun 2025 00:31:46 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 55D7VjwM3704239 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025052101; t=1749799910; bh=krbuP/fm6w7WAkYJYWFwpvmZlC0fDISskA1NKizA7xQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ssHkh09EYcaM0Ax6sdq6MtHrSSxYTaTdcsnzbRZgcdG+Isq/WnrBYczUvXTg5CwxN pcVjrm3xKQn0yhcf7jb4dEx6sAKdEgZR2whPfrJi89pD9zuGgdch3sodHzB0WrMC7R znHrQnL1Zvv+QUqFkfvmElRpjUN5lFqBkpRJm4PrSkrsX90V3GU0gMSIA7JFCrIutu PwNP6YQlhIiu/pootMO99LR+3o2402BhzCDOvvFgc9nC53bLkUx4x+coky0NVxfIxv 7y4XiCFqoDT400d95pn8JvIEA/eXVRCbaX7CtNG3q80d78+ryMmj16UFMuEHvO2ytx T+ZJnfwKScM6Q== Message-ID: <0c2dab1d-9b5c-4d34-af0e-8a14907d7335@zytor.com> Date: Fri, 13 Jun 2025 00:31:44 -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 5/6] x86/paravirt: Switch MSR access pv_ops functions to instruction interfaces To: Juergen Gross , linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev Cc: Ajay Kaher , Broadcom internal kernel review list , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Boris Ostrovsky , xen-devel@lists.xenproject.org, Andrew Cooper 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> <2365af70-d36f-4663-b819-59d886936ef5@zytor.com> <8a82946a-6c3e-41d1-b3bd-be164dc6eeba@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: <8a82946a-6c3e-41d1-b3bd-be164dc6eeba@suse.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 6/11/2025 5:58 AM, Juergen Gross wrote: >> Here is a patch I cooked.  I added an ALTERNATIVE() hack because the >> new instructions can't be more than 6 bytes long.  But with the patch you >> just sent, it shouldn't be needed. > > I have meanwhile dropped the patch copying the original indirect call. > > Reason is that I'm seeing a potential risk with current alternative > patching when using ALTERNATIVE_[23](): depending on the tested features > it might happen that an instruction sequence not suitable for the current > runtime environment is patched in as an intermediate step. In case there > is an interrupt happening just then AND the handling of the interrupt is > using the patch site, this could result in crashes or undefined behavior. Oh, I had assumed that Linux disables interrupts during the patching process. Just out of curiosity, why are interrupts allowed in this case? > > I have meanwhile a set of 3 patches fixing that problem by merging all > alternative patching of a patch site in the local buffer and only then > patching the code at the target site with the final result. > > The same problem arises with your code below, but this time it isn't > fixed by my patches: the two ALTERNATIVE() instances in the asm() construct > would need to be patched in a single atomic operation to be consistent. > Otherwise you could end up e.g. on bare metal with paravirt_read_msr() > having replaced the indirect call with "rdmsr", but not yet having added > the code to merge %rdx into %rax. > > I'm just doing a V2 of my series, but this time including the additional > support of the non-serializing and immediate forms. Lets see how this will > look like. I will drop using the EAX_EDX_* macros, but due to the reason > mentioned above I won't switch to your variant completely. Great! Thanks! Xin