From: "Li, Xin3" <xin3.li@intel.com>
To: "Li, Xin3" <xin3.li@intel.com>, "Gao, Chao" <chao.gao@intel.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kselftest@vger.kernel.org"
<linux-kselftest@vger.kernel.org>,
"seanjc@google.com" <seanjc@google.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"corbet@lwn.net" <corbet@lwn.net>,
"kys@microsoft.com" <kys@microsoft.com>,
"haiyangz@microsoft.com" <haiyangz@microsoft.com>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"Cui, Dexuan" <decui@microsoft.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"vkuznets@redhat.com" <vkuznets@redhat.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>
Subject: RE: [PATCH v1 11/23] KVM: x86: Add kvm_is_fred_enabled()
Date: Mon, 20 Nov 2023 09:04:57 +0000 [thread overview]
Message-ID: <SA1PR11MB6734703499EB40E2CB7B0D0DA8B4A@SA1PR11MB6734.namprd11.prod.outlook.com> (raw)
In-Reply-To: <SA1PR11MB6734EBD796D139957BFF2457A8B2A@SA1PR11MB6734.namprd11.prod.outlook.com>
> > >> FRED is enabled when CR4.FRED = IA32_EFER.LMA = 1. Any reason to
> > >> omit the check about long mode?
> > >
> > >It won' t allow CR4.FRED to be set if not in long mode, I don't
> > >expect it at runtime. Or you have one?
> >
> > I was thinking about a very contrived case:
> >
> > 1. the CPU enters 64-bit long mode and sets CR4.FRED 2. the CPU
> > switches out of 64-bit long mode
Actually, SDM3 Section 10.8.5 Initializing IA-32e Mode says: 64-bit mode
consistency checks fail on attempts to enable or disable IA-32e mode
while paging is enabled. In another word, the CPU allows software to
modify IA32_EFER.LME only when CR0.PG = 0 (i.e., only in legacy mode).
Thus, attempts to do so when CR0.PG = 1 will cause #GP.
Remember FRED only works with 64-bit kernel, which can be entered only
if paging is enabled. As such, to clear IA32_EFER.LME, OS/VMM needs to
turn off paging first. And to turn off paging, 64-bit mode needs to be
turned off (to enter compatibility mode in ring 0 because it's not allowed
to disable paging in 64-bit mode). Thus CR4.FRED needs be cleared first.
So CR4.FRED fully indicates whether FRED is enabled or not, which is
why FRED spec 5.0 section 9.5 says so. But we can put more explanation
there.
next prev parent reply other threads:[~2023-11-20 9:05 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-08 18:29 [PATCH v1 00/23] Enable FRED with KVM VMX Xin Li
2023-11-08 18:29 ` [PATCH v1 01/23] KVM: VMX: Cleanup VMX basic information defines and usages Xin Li
2023-11-08 18:29 ` [PATCH v1 02/23] KVM: VMX: Cleanup VMX misc " Xin Li
2023-11-08 18:29 ` [PATCH v1 03/23] KVM: VMX: Add support for the secondary VM exit controls Xin Li
2023-11-08 18:29 ` [PATCH v1 04/23] KVM: x86: Mark CR4.FRED as not reserved Xin Li
2023-11-08 18:29 ` [PATCH v1 05/23] KVM: VMX: Initialize FRED VM entry/exit controls in vmcs_config Xin Li
2023-11-09 8:53 ` Chao Gao
2023-11-09 15:15 ` Sean Christopherson
2023-11-10 0:04 ` Li, Xin3
2023-11-10 15:01 ` Sean Christopherson
2023-11-14 4:05 ` Li, Xin3
2023-11-13 17:18 ` Nikolay Borisov
2023-11-15 2:39 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 06/23] KVM: VMX: Defer enabling FRED MSRs save/load until after set CPUID Xin Li
2023-11-09 9:15 ` Chao Gao
2023-11-09 23:50 ` Li, Xin3
2023-11-10 0:18 ` Sean Christopherson
2023-11-14 2:50 ` Li, Xin3
2023-11-15 21:47 ` Sean Christopherson
2023-11-08 18:29 ` [PATCH v1 07/23] KVM: VMX: Disable intercepting FRED MSRs Xin Li
2023-11-09 9:21 ` Chao Gao
2023-11-08 18:29 ` [PATCH v1 08/23] KVM: VMX: Initialize VMCS FRED fields Xin Li
2023-11-13 3:04 ` Chao Gao
2023-11-14 6:02 ` Li, Xin3
2023-11-14 6:51 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 09/23] KVM: VMX: Switch FRED RSP0 between host and guest Xin Li
2023-11-13 3:47 ` Chao Gao
2023-11-14 5:17 ` Li, Xin3
2023-11-14 7:47 ` Chao Gao
2023-11-15 3:04 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 10/23] KVM: VMX: Add support for FRED context save/restore Xin Li
2023-11-13 5:24 ` Chao Gao
2023-11-14 4:48 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 11/23] KVM: x86: Add kvm_is_fred_enabled() Xin Li
2023-11-13 7:35 ` Chao Gao
2023-11-14 4:42 ` Li, Xin3
2023-11-14 8:16 ` Chao Gao
2023-11-14 18:57 ` Li, Xin3
2023-11-20 9:04 ` Li, Xin3 [this message]
2023-11-08 18:29 ` [PATCH v1 12/23] KVM: VMX: Handle FRED event data Xin Li
2023-11-13 10:14 ` Chao Gao
2023-11-14 4:34 ` Li, Xin3
2023-11-14 8:58 ` Chao Gao
2023-11-15 2:52 ` Li, Xin3
2023-11-16 2:39 ` Chao Gao
2023-11-20 8:16 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 13/23] KVM: VMX: Handle VMX nested exception for FRED Xin Li
2023-11-14 7:40 ` Chao Gao
2023-11-15 3:03 ` Li, Xin3
2023-12-06 8:37 ` Li, Xin3
2023-12-07 8:42 ` Chao Gao
2023-12-07 10:09 ` Li, Xin3
2023-12-08 1:56 ` Chao Gao
2023-12-08 23:48 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 14/23] KVM: VMX: Dump FRED context in dump_vmcs() Xin Li
2023-11-14 14:36 ` Nikolay Borisov
2023-11-15 2:41 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 15/23] KVM: nVMX: Add support for the secondary VM exit controls Xin Li
2023-11-09 8:21 ` Jeremi Piotrowski
2023-11-10 0:12 ` Li, Xin3
2023-11-20 15:52 ` Vitaly Kuznetsov
2023-11-20 17:42 ` Li, Xin3
2023-11-08 18:29 ` [PATCH v1 16/23] KVM: nVMX: Add FRED VMCS fields Xin Li
2023-11-08 18:29 ` [PATCH v1 17/23] KVM: nVMX: Add support for VMX FRED controls Xin Li
2023-11-08 18:29 ` [PATCH v1 18/23] KVM: nVMX: Add VMCS FRED states checking Xin Li
2023-11-08 18:29 ` [PATCH v1 19/23] KVM: x86: Allow FRED/LKGS/WRMSRNS to be exposed to guests Xin Li
2023-11-08 18:30 ` [PATCH v1 20/23] KVM: selftests: Add FRED VMCS fields to evmcs Xin Li
2023-11-08 18:30 ` [PATCH v1 21/23] KVM: selftests: Run debug_regs test with FRED enabled Xin Li
2023-11-08 18:30 ` [PATCH v1 22/23] KVM: selftests: Add a new VM guest mode to run user level code Xin Li
2023-11-08 18:30 ` [PATCH v1 23/23] KVM: selftests: Add fred exception tests Xin Li
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