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X-CSE-ConnectionGUID: znI0cZSkTrS8+psuDA6xkw== X-CSE-MsgGUID: kFMrd8a2Tm+rY9NIg9Huiw== X-IronPort-AV: E=McAfee;i="6800,10657,11673"; a="80551483" X-IronPort-AV: E=Sophos;i="6.21,232,1763452800"; d="scan'208";a="80551483" Received: from fmviesa007.fm.intel.com ([10.60.135.147]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2026 11:50:05 -0800 X-CSE-ConnectionGUID: 5EWABOIQSF+CRKRCNGqU3A== X-CSE-MsgGUID: /3hpLGnDSGW7SWb9/+MYmQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,232,1763452800"; d="scan'208";a="204939094" Received: from gabaabhi-mobl2.amr.corp.intel.com (HELO [10.125.111.136]) ([10.125.111.136]) by fmviesa007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2026 11:49:58 -0800 Message-ID: Date: Fri, 16 Jan 2026 11:49:53 -0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 08/22] KVM: VMX: Set FRED MSR intercepts To: "Xin Li (Intel)" , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org Cc: pbonzini@redhat.com, seanjc@google.com, corbet@lwn.net, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, andrew.cooper3@citrix.com, chao.gao@intel.com, hch@infradead.org, sohil.mehta@intel.com References: <20251026201911.505204-1-xin@zytor.com> <20251026201911.505204-9-xin@zytor.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/26/25 13:18, Xin Li (Intel) wrote: > Both MSR_IA32_FRED_RSP0 and MSR_IA32_FRED_SSP0 (aka MSR_IA32_PL0_SSP) > are dedicated for userspace event delivery, IOW they are NOT used in > any kernel event delivery and the execution of ERETS. Thus KVM can > run safely with guest values in the two MSRs. As a result, save and > restore of their guest values are deferred until vCPU context switch, > Host MSR_IA32_FRED_RSP0 is restored upon returning to userspace, and > Host MSR_IA32_PL0_SSP is managed with XRSTORS/XSAVES. Is it worth making MSR_IA32_FRED_RSP0 special versus MSR_IA32_FRED_RSP[123]? Is it needed because MSR_IA32_FRED_RSP0 is rewritten all the time as CPUs switch between threads? But MSR_IA32_FRED_RSP[123] are not frequently written? I'd like to hear more about the motivation.