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    SubjectRe: [PATCH v2 24/28] KVM: nVMX: Use sanitized allowed-1 bits for VMX control MSRs
    On Wed, Jun 29, 2022 at 8:07 AM Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
    >
    > Using raw host MSR values for setting up nested VMX control MSRs is
    > incorrect as some features need to disabled, e.g. when KVM runs as
    > a nested hypervisor on Hyper-V and uses Enlightened VMCS or when a
    > workaround for IA32_PERF_GLOBAL_CTRL is applied. For non-nested VMX, this
    > is done in setup_vmcs_config() and the result is stored in vmcs_config.
    > Use it for setting up allowed-1 bits in nested VMX MSRs too.
    >
    > Suggested-by: Sean Christopherson <seanjc@google.com>
    > Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    > ---
    > arch/x86/kvm/vmx/nested.c | 34 ++++++++++++++++------------------
    > arch/x86/kvm/vmx/nested.h | 2 +-
    > arch/x86/kvm/vmx/vmx.c | 5 ++---
    > 3 files changed, 19 insertions(+), 22 deletions(-)
    >
    > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
    > index 88625965f7b7..e5b19b5e6cab 100644
    > --- a/arch/x86/kvm/vmx/nested.c
    > +++ b/arch/x86/kvm/vmx/nested.c
    > @@ -6565,8 +6565,13 @@ static u64 nested_vmx_calc_vmcs_enum_msr(void)
    > * bit in the high half is on if the corresponding bit in the control field
    > * may be on. See also vmx_control_verify().
    > */
    > -void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
    > +void nested_vmx_setup_ctls_msrs(struct vmcs_config *vmcs_conf, u32 ept_caps)
    > {
    > + struct nested_vmx_msrs *msrs = &vmcs_conf->nested;
    > +
    > + /* Take the allowed-1 bits from KVM's sanitized VMCS configuration. */
    > + u32 ignore_high;
    > +

    Giving this object a name seems gauche.

    > /*
    > * Note that as a general rule, the high half of the MSRs (bits in
    > * the control fields which may be 1) should be initialized by the
    > @@ -6583,11 +6588,11 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
    > */
    >
    > /* pin-based controls */
    > - rdmsr(MSR_IA32_VMX_PINBASED_CTLS,
    > - msrs->pinbased_ctls_low,
    > - msrs->pinbased_ctls_high);
    > + rdmsr(MSR_IA32_VMX_PINBASED_CTLS, msrs->pinbased_ctls_low, ignore_high);

    Perhaps "(u32){0}" rather than "ignore_high"?

    > msrs->pinbased_ctls_low |=
    > PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR;

    NYC, but why is this one '|=', and the rest just '='? Does there exist
    a CPU that requires more than PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR?

    > +
    > + msrs->pinbased_ctls_high = vmcs_conf->pin_based_exec_ctrl;
    > msrs->pinbased_ctls_high &=
    > PIN_BASED_EXT_INTR_MASK |
    > PIN_BASED_NMI_EXITING |
    > @@ -6598,12 +6603,10 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
    > PIN_BASED_VMX_PREEMPTION_TIMER;
    >
    > /* exit controls */
    > - rdmsr(MSR_IA32_VMX_EXIT_CTLS,
    > - msrs->exit_ctls_low,
    > - msrs->exit_ctls_high);
    > msrs->exit_ctls_low =
    > VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
    >
    > + msrs->exit_ctls_high = vmcs_conf->vmexit_ctrl;
    > msrs->exit_ctls_high &=
    > #ifdef CONFIG_X86_64
    > VM_EXIT_HOST_ADDR_SPACE_SIZE |
    > @@ -6619,11 +6622,10 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
    > msrs->exit_ctls_low &= ~VM_EXIT_SAVE_DEBUG_CONTROLS;
    >
    > /* entry controls */
    > - rdmsr(MSR_IA32_VMX_ENTRY_CTLS,
    > - msrs->entry_ctls_low,
    > - msrs->entry_ctls_high);
    > msrs->entry_ctls_low =
    > VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR;
    > +
    > + msrs->entry_ctls_high = vmcs_conf->vmentry_ctrl;
    > msrs->entry_ctls_high &=
    > #ifdef CONFIG_X86_64
    > VM_ENTRY_IA32E_MODE |
    > @@ -6637,11 +6639,10 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
    > msrs->entry_ctls_low &= ~VM_ENTRY_LOAD_DEBUG_CONTROLS;
    >
    > /* cpu-based controls */
    > - rdmsr(MSR_IA32_VMX_PROCBASED_CTLS,
    > - msrs->procbased_ctls_low,
    > - msrs->procbased_ctls_high);
    > msrs->procbased_ctls_low =
    > CPU_BASED_ALWAYSON_WITHOUT_TRUE_MSR;
    > +
    > + msrs->procbased_ctls_high = vmcs_conf->cpu_based_exec_ctrl;
    > msrs->procbased_ctls_high &=
    > CPU_BASED_INTR_WINDOW_EXITING |
    > CPU_BASED_NMI_WINDOW_EXITING | CPU_BASED_USE_TSC_OFFSETTING |
    > @@ -6675,12 +6676,9 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
    > * depend on CPUID bits, they are added later by
    > * vmx_vcpu_after_set_cpuid.
    > */
    > - if (msrs->procbased_ctls_high & CPU_BASED_ACTIVATE_SECONDARY_CONTROLS)
    > - rdmsr(MSR_IA32_VMX_PROCBASED_CTLS2,
    > - msrs->secondary_ctls_low,
    > - msrs->secondary_ctls_high);
    > -
    > msrs->secondary_ctls_low = 0;
    > +
    > + msrs->secondary_ctls_high = vmcs_conf->cpu_based_2nd_exec_ctrl;
    > msrs->secondary_ctls_high &=
    > SECONDARY_EXEC_DESC |
    > SECONDARY_EXEC_ENABLE_RDTSCP |
    > diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
    > index c92cea0b8ccc..fae047c6204b 100644
    > --- a/arch/x86/kvm/vmx/nested.h
    > +++ b/arch/x86/kvm/vmx/nested.h
    > @@ -17,7 +17,7 @@ enum nvmx_vmentry_status {
    > };
    >
    > void vmx_leave_nested(struct kvm_vcpu *vcpu);
    > -void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps);
    > +void nested_vmx_setup_ctls_msrs(struct vmcs_config *vmcs_conf, u32 ept_caps);
    > void nested_vmx_hardware_unsetup(void);
    > __init int nested_vmx_hardware_setup(int (*exit_handlers[])(struct kvm_vcpu *));
    > void nested_vmx_set_vmcs_shadowing_bitmap(void);
    > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
    > index 5f7ef1f8d2c6..5d4158b7421c 100644
    > --- a/arch/x86/kvm/vmx/vmx.c
    > +++ b/arch/x86/kvm/vmx/vmx.c
    > @@ -7310,7 +7310,7 @@ static int __init vmx_check_processor_compat(void)
    > if (setup_vmcs_config(&vmcs_conf, &vmx_cap) < 0)
    > return -EIO;
    > if (nested)
    > - nested_vmx_setup_ctls_msrs(&vmcs_conf.nested, vmx_cap.ept);
    > + nested_vmx_setup_ctls_msrs(&vmcs_conf, vmx_cap.ept);
    > if (memcmp(&vmcs_config, &vmcs_conf, sizeof(struct vmcs_config)) != 0) {
    > printk(KERN_ERR "kvm: CPU %d feature inconsistency!\n",
    > smp_processor_id());
    > @@ -8285,8 +8285,7 @@ static __init int hardware_setup(void)
    > setup_default_sgx_lepubkeyhash();
    >
    > if (nested) {
    > - nested_vmx_setup_ctls_msrs(&vmcs_config.nested,
    > - vmx_capability.ept);
    > + nested_vmx_setup_ctls_msrs(&vmcs_config, vmx_capability.ept);
    >
    > r = nested_vmx_hardware_setup(kvm_vmx_exit_handlers);
    > if (r)
    > --
    > 2.35.3
    >

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