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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=dtjjIfU0jwte8iB+16b3u9aCi45gWHmC3k277R/avs9h9Zg0QkQ/8xjtzAe0saMP7 vKo69yEK9wm+Xq73m4AskoAss7DFNTl3muUjEqkuFiNe82oh/3q9gilYjsAciLIOQQ R0J3o4azFBaOmXLyPLOBVT6KoSol+20KO9IlcJop41L+zvBEUM3DDOuf3vEnyhRj9+ OPxUwwHSauda8lVW1jO7cZHtY8j32IMjvM6KkV7J1PJ58kObBoi7qeBJQ3yuD7uaAX CvciviQ4ztHKtRrarLRAryyYomrrfZMrthuHWPI/VR1QNIYKwg+ylAY/oz63BJcvOW DCi9QTs2SFD9g== Message-ID: Date: Fri, 25 Oct 2024 00:25:45 -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 v3 25/27] KVM: nVMX: Add FRED VMCS fields To: Chao Gao Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, seanjc@google.com, pbonzini@redhat.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 References: <20241001050110.3643764-1-xin@zytor.com> <20241001050110.3643764-26-xin@zytor.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 10/24/2024 12:42 AM, Chao Gao wrote: >> @@ -7197,6 +7250,9 @@ static void nested_vmx_setup_basic(struct nested_vmx_msrs *msrs) >> msrs->basic |= VMX_BASIC_TRUE_CTLS; >> if (cpu_has_vmx_basic_inout()) >> msrs->basic |= VMX_BASIC_INOUT; >> + >> + if (cpu_has_vmx_fred()) >> + msrs->basic |= VMX_BASIC_NESTED_EXCEPTION; > > why not advertising VMX_BASIC_NESTED_EXCEPTION if the CPU supports it? just like > VMX_BASIC_INOUT right above. Because VMX nested-exception support only works with FRED. We could pass host MSR_IA32_VMX_BASIC.VMX_BASIC_NESTED_EXCEPTION to nested, but it's meaningless w/o VMX FRED. > > >> } >> >> static void nested_vmx_setup_cr_fixed(struct nested_vmx_msrs *msrs) >> diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h >> index 2c296b6abb8c..5272f617fcef 100644 >> --- a/arch/x86/kvm/vmx/nested.h >> +++ b/arch/x86/kvm/vmx/nested.h >> @@ -251,6 +251,14 @@ static inline bool nested_cpu_has_encls_exit(struct vmcs12 *vmcs12) >> return nested_cpu_has2(vmcs12, SECONDARY_EXEC_ENCLS_EXITING); >> } >> >> +static inline bool nested_cpu_has_fred(struct vmcs12 *vmcs12) >> +{ >> + return vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_FRED && >> + vmcs12->vm_exit_controls & VM_EXIT_ACTIVATE_SECONDARY_CONTROLS && >> + vmcs12->secondary_vm_exit_controls & SECONDARY_VM_EXIT_SAVE_IA32_FRED && >> + vmcs12->secondary_vm_exit_controls & SECONDARY_VM_EXIT_LOAD_IA32_FRED; > > Is it a requirement in the SDM that the VMM should enable all FRED controls or > none? If not, the VMM is allowed to enable only one or two of them. This means > KVM would need to emulate FRED controls for the L1 VMM as three separate > features. The SDM doesn't say that. But FRED states are used during and immediately after VM entry and exit, I don't see a good reason for a VMM to enable only one or two of the 3 save/load configs. Say if VM_ENTRY_LOAD_IA32_FRED is not set, it means a VMM needs to switch to guest FRED states before it does a VM entry, which is absolutely a big mess. TBH I'm not sure this is the question you have in mind.