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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id l23sm22961827wmh.40.2020.11.30.05.54.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Nov 2020 05:54:02 -0800 (PST) Subject: Re: [PATCH 2/2] KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS To: Maxim Levitsky , kvm@vger.kernel.org Cc: Oliver Upton , Ingo Molnar , Sean Christopherson , Thomas Gleixner , open list , Marcelo Tosatti , Jonathan Corbet , Wanpeng Li , Borislav Petkov , Jim Mattson , "H. Peter Anvin" , "open list:DOCUMENTATION" , Joerg Roedel , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Vitaly Kuznetsov References: <20201130133559.233242-1-mlevitsk@redhat.com> <20201130133559.233242-3-mlevitsk@redhat.com> From: Paolo Bonzini Message-ID: Date: Mon, 30 Nov 2020 14:54:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201130133559.233242-3-mlevitsk@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/11/20 14:35, Maxim Levitsky wrote: > This quirk reflects the fact that we currently treat MSR_IA32_TSC > and MSR_TSC_ADJUST access by the host (e.g qemu) in a way that is different > compared to an access from the guest. > > For host's MSR_IA32_TSC read we currently always return L1 TSC value, and for > host's write we do the tsc synchronization. > > For host's MSR_TSC_ADJUST write, we don't make the tsc 'jump' as we should > for this msr. > > When the hypervisor uses the new TSC GET/SET state ioctls, all of this is no > longer needed, thus leave this enabled only with a quirk > which the hypervisor can disable. > > Suggested-by: Paolo Bonzini > Signed-off-by: Maxim Levitsky This needs to be covered by a variant of the existing selftests testcase (running the same guest code, but different host code of course). Paolo > --- > arch/x86/include/uapi/asm/kvm.h | 1 + > arch/x86/kvm/x86.c | 19 ++++++++++++++----- > 2 files changed, 15 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h > index 8e76d3701db3f..2a60fc6674164 100644 > --- a/arch/x86/include/uapi/asm/kvm.h > +++ b/arch/x86/include/uapi/asm/kvm.h > @@ -404,6 +404,7 @@ struct kvm_sync_regs { > #define KVM_X86_QUIRK_LAPIC_MMIO_HOLE (1 << 2) > #define KVM_X86_QUIRK_OUT_7E_INC_RIP (1 << 3) > #define KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT (1 << 4) > +#define KVM_X86_QUIRK_TSC_HOST_ACCESS (1 << 5) > > #define KVM_STATE_NESTED_FORMAT_VMX 0 > #define KVM_STATE_NESTED_FORMAT_SVM 1 > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 4f0ae9cb14b8a..46a2111d54840 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -3091,7 +3091,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > break; > case MSR_IA32_TSC_ADJUST: > if (guest_cpuid_has(vcpu, X86_FEATURE_TSC_ADJUST)) { > - if (!msr_info->host_initiated) { > + if (!msr_info->host_initiated || > + !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TSC_HOST_ACCESS)) { > s64 adj = data - vcpu->arch.ia32_tsc_adjust_msr; > adjust_tsc_offset_guest(vcpu, adj); > } > @@ -3118,7 +3119,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > vcpu->arch.msr_ia32_power_ctl = data; > break; > case MSR_IA32_TSC: > - if (msr_info->host_initiated) { > + if (msr_info->host_initiated && > + kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TSC_HOST_ACCESS)) { > kvm_synchronize_tsc(vcpu, data); > } else { > u64 adj = kvm_compute_tsc_offset(vcpu, data) - vcpu->arch.l1_tsc_offset; > @@ -3409,17 +3411,24 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > msr_info->data = vcpu->arch.msr_ia32_power_ctl; > break; > case MSR_IA32_TSC: { > + u64 tsc_offset; > + > /* > * Intel SDM states that MSR_IA32_TSC read adds the TSC offset > * even when not intercepted. AMD manual doesn't explicitly > * state this but appears to behave the same. > * > - * On userspace reads and writes, however, we unconditionally > + * On userspace reads and writes, when KVM_X86_QUIRK_SPECIAL_TSC_READ > + * is present, however, we unconditionally > * return L1's TSC value to ensure backwards-compatible > * behavior for migration. > */ > - u64 tsc_offset = msr_info->host_initiated ? vcpu->arch.l1_tsc_offset : > - vcpu->arch.tsc_offset; > + > + if (msr_info->host_initiated && > + kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_TSC_HOST_ACCESS)) > + tsc_offset = vcpu->arch.l1_tsc_offset; > + else > + tsc_offset = vcpu->arch.tsc_offset; > > msr_info->data = kvm_scale_tsc(vcpu, rdtsc()) + tsc_offset; > break; >