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h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=rFfZBdH1011mTnLueI/EDslLu0GpRaP2Tf/VuxRLEa/LR3j2uQkmtB94yYKQiTIe3 lLnxhbqiK01Pzki3pIoKzKhddPoP8rMnSsX3nfnbuL57st5BBapBV6Lr3hJbBCZ/Ft vkM9vm6+wMGu3f0/nN8yzKlN2iNieRT6iLObqQD4dR5Vg+xyWLxrTdWp6rvBe1Jrq4 zNmEoaGQx3rEYto24d4FxywDIU9lcSW1W1UCRyLIsjAksWRAJPcvlUtIIsuAyPBVL/ jUz75YkoTxJ9TlmeHXMeJzeDsmK+pFTlVvU9OAZi5eVpCwLKkooioOMmu3HAZnd6/A AvadKtJCljKgQ== Message-ID: <5ca5d98e-6a3c-48fc-8aa2-7db0980543e6@zytor.com> Date: Sun, 3 Aug 2025 23:03:16 -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 v5A 20/23] KVM: nVMX: Add FRED VMCS fields to nested VMX context handling From: Xin Li To: 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 References: <20250802171740.3677712-1-xin@zytor.com> Content-Language: en-US Autocrypt: addr=xin@zytor.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/2/2025 10:33 AM, Xin Li wrote: >> @@ -4531,6 +4593,27 @@ static void sync_vmcs02_to_vmcs12_rare(struct >> kvm_vcpu *vcpu, >>       vmcs12->guest_tr_base = vmcs_readl(GUEST_TR_BASE); >>       vmcs12->guest_gdtr_base = vmcs_readl(GUEST_GDTR_BASE); >>       vmcs12->guest_idtr_base = vmcs_readl(GUEST_IDTR_BASE); >> + >> +    vmx->nested.pre_vmexit_fred_config = >> vmcs_read64(GUEST_IA32_FRED_CONFIG); >> +    vmx->nested.pre_vmexit_fred_rsp1 = >> vmcs_read64(GUEST_IA32_FRED_RSP1); >> +    vmx->nested.pre_vmexit_fred_rsp2 = >> vmcs_read64(GUEST_IA32_FRED_RSP2); >> +    vmx->nested.pre_vmexit_fred_rsp3 = >> vmcs_read64(GUEST_IA32_FRED_RSP3); >> +    vmx->nested.pre_vmexit_fred_stklvls = >> vmcs_read64(GUEST_IA32_FRED_STKLVLS); >> +    vmx->nested.pre_vmexit_fred_ssp1 = >> vmcs_read64(GUEST_IA32_FRED_SSP1); >> +    vmx->nested.pre_vmexit_fred_ssp2 = >> vmcs_read64(GUEST_IA32_FRED_SSP2); >> +    vmx->nested.pre_vmexit_fred_ssp3 = >> vmcs_read64(GUEST_IA32_FRED_SSP3); > > This ... > >> + >> +    if (nested_cpu_save_guest_fred_state(vmcs12)) { >> +        vmcs12->guest_ia32_fred_config = vmx- >> >nested.pre_vmexit_fred_config; >> +        vmcs12->guest_ia32_fred_rsp1 = vmx->nested.pre_vmexit_fred_rsp1; >> +        vmcs12->guest_ia32_fred_rsp2 = vmx->nested.pre_vmexit_fred_rsp2; >> +        vmcs12->guest_ia32_fred_rsp3 = vmx->nested.pre_vmexit_fred_rsp3; >> +        vmcs12->guest_ia32_fred_stklvls = vmx- >> >nested.pre_vmexit_fred_stklvls; >> +        vmcs12->guest_ia32_fred_ssp1 = vmx->nested.pre_vmexit_fred_ssp1; >> +        vmcs12->guest_ia32_fred_ssp2 = vmx->nested.pre_vmexit_fred_ssp2; >> +        vmcs12->guest_ia32_fred_ssp3 = vmx->nested.pre_vmexit_fred_ssp3; >> +    } >> + >>       vmcs12->guest_pending_dbg_exceptions = >>           vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS); >> @@ -4761,6 +4860,26 @@ static void load_vmcs12_host_state(struct >> kvm_vcpu *vcpu, >>       vmcs_write32(GUEST_IDTR_LIMIT, 0xFFFF); >>       vmcs_write32(GUEST_GDTR_LIMIT, 0xFFFF); >> +    if (nested_cpu_load_host_fred_state(vmcs12)) { >> +        vmcs_write64(GUEST_IA32_FRED_CONFIG, vmcs12- >> >host_ia32_fred_config); >> +        vmcs_write64(GUEST_IA32_FRED_RSP1, vmcs12->host_ia32_fred_rsp1); >> +        vmcs_write64(GUEST_IA32_FRED_RSP2, vmcs12->host_ia32_fred_rsp2); >> +        vmcs_write64(GUEST_IA32_FRED_RSP3, vmcs12->host_ia32_fred_rsp3); >> +        vmcs_write64(GUEST_IA32_FRED_STKLVLS, vmcs12- >> >host_ia32_fred_stklvls); >> +        vmcs_write64(GUEST_IA32_FRED_SSP1, vmcs12->host_ia32_fred_ssp1); >> +        vmcs_write64(GUEST_IA32_FRED_SSP2, vmcs12->host_ia32_fred_ssp2); >> +        vmcs_write64(GUEST_IA32_FRED_SSP3, vmcs12->host_ia32_fred_ssp3); >> +    } else { >> +        vmcs_write64(GUEST_IA32_FRED_CONFIG, vmx- >> >nested.pre_vmexit_fred_config); >> +        vmcs_write64(GUEST_IA32_FRED_RSP1, vmx- >> >nested.pre_vmexit_fred_rsp1); >> +        vmcs_write64(GUEST_IA32_FRED_RSP2, vmx- >> >nested.pre_vmexit_fred_rsp2); >> +        vmcs_write64(GUEST_IA32_FRED_RSP3, vmx- >> >nested.pre_vmexit_fred_rsp3); >> +        vmcs_write64(GUEST_IA32_FRED_STKLVLS, vmx- >> >nested.pre_vmexit_fred_stklvls); >> +        vmcs_write64(GUEST_IA32_FRED_SSP1, vmx- >> >nested.pre_vmexit_fred_ssp1); >> +        vmcs_write64(GUEST_IA32_FRED_SSP2, vmx- >> >nested.pre_vmexit_fred_ssp2); >> +        vmcs_write64(GUEST_IA32_FRED_SSP3, vmx- >> >nested.pre_vmexit_fred_ssp3); > > And this are actually nops. IOW, if I don't add this snippet of code, > the CPU still retains the guest FRED MSRs, i.e., using guest FRED state > from vmcs02 as that of vmcs01. I confused myself. They are NOT nops, because __nested_vmx_vmexit() switches from vmcs02 to vmcs01. The code should be (as the patch does): __nested_vmx_vmexit() { ... /* * Save guest FRED state of vmcs02 to nested.pre_vmexit_fred * no matter if SECONDARY_VM_EXIT_SAVE_IA32_FRED is set. */ sync_vmcs02_to_vmcs12(); ... vmx_switch_vmcs(); ... /* * Load nested.pre_vmexit_fred to guest FRED state of vmcs01 * if SECONDARY_VM_EXIT_LOAD_IA32_FRED is NOT set. */ load_vmcs12_host_state(); ... } As not setting any of the two FRED VM-Exit controls are rare cases, we need to add KVM tests with L1 that: 1) doesn't set SECONDARY_VM_EXIT_SAVE_IA32_FRED in VM-Exit controls. 2) doesn't set SECONDARY_VM_EXIT_LOAD_IA32_FRED in VM-Exit controls. 3) doesn't set both of the FRED VM-Exit controls. Looks we need a framework for all VM-Exit controls which control whether to save/load specific MSRs related to CPU features during VM-Exit?