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 38A9C204C2B for ; Wed, 8 Jan 2025 23:33:18 +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=1736379199; cv=none; b=HXgIFrjzgYoBQ8dDZY1B35GOoY7mlPnAY1qwfHcBDRYjF6FDNrVnBOJl357IXWQrMvp906+QFQw4oeTE7p77cCT+6MBKSRacYaC8KnweDRcxXm522Ug5VqzRw+hwj4elSvN2EJaklC5mafKeQjMxV8bnvMBH0/DyfaXIuj9OD/A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736379199; c=relaxed/simple; bh=yaQRu7bActiqVfuliLN5x6Dyu8IODKAbwWR2HHFZWBI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uE0taFFFnlVL0eGqHgP1RIFdh2NFH3T/LYEE/577N/o/w/ymDc076XpH5zZftdb1x0oHsuzSK+6ojSZ7dwbCYD9B9MId2biTNkwNAKIeF2SDgW0r7jaxlx66LlYiUjBdI4nQNIum8Slf0wSvaXZQOwgwjDBBgF2MZTgHMCFnlqQ= ARC-Authentication-Results:i=1; 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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=T4OgjRI1mhpg6mRYwg3rariCzhXZKsXUyAtm3cSWx/aQqyDZM0jvf5CgGmpIGEAPt nENfKEls43GU9Qgq5oflj9NBa0aspyzTcTSVmFvbgRq1wf8K23u0clERitc+KSepJp gsz7QQSFSXIOIo7aYHZZMXnITqC9ti36+JLSCV/lUrJ5ehUUYuDOmU0mFY/ZsH28xz ZcLOQkME3N4/7S6QEUvAOpgsjo2lHqPxXHm0WNdFxC/hKgxnFgd1iHGE1Ttrm/yPKe 3OIcGI8zi79ssXPbHr/s7VVevT20ETtERSrXEPlfNtcKz6Rpww/ve7t3/zzLiBxSKy KK1hD/SwBwnNQ== Message-ID: <2402fe84-a511-4178-94a3-28f926a96c7c@zytor.com> Date: Wed, 8 Jan 2025 15:32:58 -0800 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 1/1] x86/fred: Fix the FRED RSP0 MSR out of sync with its per CPU cache To: Dave Hansen , Andrew Cooper , linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com References: <20250108023641.17396-1-xin@zytor.com> <45d4edfd-d3d9-4115-9ec3-947630b06ce0@intel.com> Content-Language: en-US From: Xin Li Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/8/2025 2:31 PM, Dave Hansen wrote: > On 1/8/25 13:10, Andrew Cooper wrote: >> On 08/01/2025 8:14 pm, Dave Hansen wrote: >>> On 1/7/25 18:36, Xin Li (Intel) wrote: >>>> + * Another option is to leave the FRED RSP0 MSR as-is, because the RESET >>>> + * state of FRED MSRs is zero and INIT does not change the value of the >>>> + * FRED MSRs in a CPU offline/online cycle. But it doesn't seem safe to >>>> + * depend on the properties of INIT as that's way too many things that >>>> + * could cause bugs. >>> Wouldn't that also open us up to kexec problems? If the last kernel >>> (maybe not even Linux) left RSP0 set, then the current kernel might >>> eventually try to run userspace with the old kernel's RSP0 value. >> That's why the init code needs to write every control MSR, even if it's >> filling in 0 because it doesn't want to use the feature. >> >> The job of the init code is to go from an unknown state into a good >> state, not from the INIT/#RESET state. > > Right, so I think the quoted "Another option..." comment needs to get > zapped. Because it's not really another option. Discussing alternatives > is better left for changelogs anyway, not code comments. > Will do!