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 14351802 for ; Thu, 4 Jul 2024 00:20:57 +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=1720052460; cv=none; b=fekkx/fiT0a0g4FGALLFSTEDyGtvI4l/gw6UUjNZfq9CFU/8g4DuRLreTNdpkBFW4e6uMZhEtENU2ckda86hpsWdF8Hgv5Vl5Mlcp/v73VxFyMEmjPNSE1kf1CMyDVUBPrb9Vl0kIx37w+hfkiLdlsSdNXW6cHme6EpfDzI1i2c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720052460; c=relaxed/simple; bh=6KK7oTY/cTJHENP66oVTWy9znLaOryTeOiG1rRIYNcU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jen0hqP7mb6rzK6+2QSKftjGQyyyRVII2YRuns+i4f3uCXgBdcDvA13uGKRKtI2sBW82aI8bHtdeHqO0tLMwHo+fjDFbpZE1Hj64YZkp3/aISS4JJ7YNmy5KUwfJnQuz1wg6SYbCXS4vp0k1Y2lh2M12lroo1aUttwGhickNcMM= 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=M+lS2mKo; 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="M+lS2mKo" Received: from [192.168.7.205] ([71.202.166.45]) (authenticated bits=0) by mail.zytor.com (8.17.2/8.17.1) with ESMTPSA id 463Mm4C21070766 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Wed, 3 Jul 2024 15:48:05 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 463Mm4C21070766 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2024061501; t=1720046886; bh=Mt7iDqDbKs8II8sIWBE5dbgK5jzEx5l8Qan/TPvdsXc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=M+lS2mKo5BsSrDDfOvlbWHP8CSfO5g3C7HHm03HUBcxP3driqF7d2WLbbuG2sARjy GOcwkdMI6pmTXU4d7m1BTkrJKjAKXm3sZ3ZM8f1HicJ3mz1auHXlulMuppkdVzEL3v VUvmsPIMOT/FNlMcp0Gs/Tv8xx187luETD1GbWO6hpaJYHIPGOn9Rb2PQKUc/xgGHY /Zl88IBRIx0ugVIV+Fc1M1+b+4w/zy9bl65p2wNWIu2m+CDL+CDzKDM6R69zlSZ7Xd cWxYB8VE71E2Gzo57VyOfHKcY6bozAQWrOkRrLA73YD0sB0GXl0nI7xbVQ1Ed9HuJS iazqfRZTcTaOQ== Message-ID: Date: Wed, 3 Jul 2024 15:48:04 -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 v1 2/4] x86/fred: Write to FRED MSRs with wrmsrns() To: Dave Hansen , "H. Peter Anvin" , Andrew Cooper , Borislav Petkov Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org, peterz@infradead.org, nik.borisov@suse.com, houwenlong.hwl@antgroup.com References: <9063b0fe-e8f3-44ff-b323-b2b6c338690f@intel.com> <172002205406.3280081.14523962650685954182@Ubuntu-2204-jammy-amd64-base> <15f56e6a-6edd-43d0-8e83-bb6430096514@citrix.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: 7bit On 7/3/2024 9:43 AM, Dave Hansen wrote: > On 7/3/24 09:06, H. Peter Anvin wrote: >> I believe tglx declared to use them unconditionally since FRED> depends on WRMSRNS (and the kernel enforces that.) > > Ahh, I forgot about: > > static const struct cpuid_dep cpuid_deps[] = { > ... > { X86_FEATURE_FRED, X86_FEATURE_WRMSRNS }, > > So, yeah, Xin's patch here is quite safe and when Boris said: > >> Also, all those wrmsrns() writes better be behind a CPUID check. > > ... it *is* behind a CPUID check, but it's an implicit one. > Right! Otherwise typically there will be two feature checks in a line in the source code (the run time code is binary patched): if (cpu_feature_enabled(X86_FEATURE_FRED)) { if (cpu_feature_enabled(X86_FEATURE_WRMSRNS)) wrmsrns(MSR_IA32_FRED_RSP0, ...); else wrmsrl(MSR_IA32_FRED_RSP0, ...); } Yes, Andrew's idea to use alternative_input() is a clean approach that everyone has agreed. However there is a more fundamental problem with how WRMSR instruction is being used in the existing code: https://lore.kernel.org/lkml/87y1h81ht4.ffs@tglx/. My rough understanding is that first we want something like: alternative_input("call paravirt_write_msr", "wrmsr", X86_FEATURE_XENPV); to get PVOPS out of the picture, and then apply alternative_input() as Andrew proposed. I thought about giving it a shot, but it never comes to the top of my task list. Thanks! Xin