Re: [Qemu-devel] [PATCH] kvm: Enable -cpu option to hide KVM

[Bandan Das]

Alex Williamson <address@hidden> writes:

> The latest Nvidia driver (337.88) specifically checks for KVM as the
> hypervisor and reports Code 43 for the driver in a Windows guest when
> found.  Removing or changing the KVM signature is sufficient for the
> driver to load and work.  This patch adds an option to easily allow
> the KVM hypervisor signature to be hidden using '-cpu kvm=off'.  We
> continue to expose KVM via the cpuid value by default.  The state of
> this option does not supercede or replace -enable-kvm or the accel=kvm
> machine option.  This only changes the visibility of KVM to the guest
> and paravirtual features specifically tied to the KVM cpuid.
>
> Signed-off-by: Alex Williamson <address@hidden>
> ---
>  target-i386/cpu-qom.h |    1 +
>  target-i386/cpu.c     |    1 +
>  target-i386/kvm.c     |   28 +++++++++++++++-------------
>  3 files changed, 17 insertions(+), 13 deletions(-)
>
> diff --git a/target-i386/cpu-qom.h b/target-i386/cpu-qom.h
> index e9b3d57..0808cfc 100644
> --- a/target-i386/cpu-qom.h
> +++ b/target-i386/cpu-qom.h
> @@ -87,6 +87,7 @@ typedef struct X86CPU {
>      bool hyperv_time;
>      bool check_cpuid;
>      bool enforce_cpuid;
> +    bool expose_kvm;
>  
>      /* if true the CPUID code directly forward host cache leaves to the 
> guest */
>      bool cache_info_passthrough;
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 042a48d..cbf1d97 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2792,6 +2792,7 @@ static Property x86_cpu_properties[] = {
>      DEFINE_PROP_BOOL("hv-time", X86CPU, hyperv_time, false),
>      DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, false),
>      DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),
> +    DEFINE_PROP_BOOL("kvm", X86CPU, expose_kvm, true),
>      DEFINE_PROP_END_OF_LIST()
>  };
>  
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 0d894ef..b2295d2 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -528,23 +528,25 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          has_msr_hv_hypercall = true;
>      }
>  
> -    memcpy(signature, "KVMKVMKVM\0\0\0", 12);
> -    c = &cpuid_data.entries[cpuid_i++];
> -    c->function = KVM_CPUID_SIGNATURE | kvm_base;
> -    c->eax = 0;
> -    c->ebx = signature[0];
> -    c->ecx = signature[1];
> -    c->edx = signature[2];
> +    if (cpu->expose_kvm) {
> +        memcpy(signature, "KVMKVMKVM\0\0\0", 12);
> +        c = &cpuid_data.entries[cpuid_i++];
> +        c->function = KVM_CPUID_SIGNATURE | kvm_base;
> +        c->eax = 0;
> +        c->ebx = signature[0];
> +        c->ecx = signature[1];
> +        c->edx = signature[2];
>  
> -    c = &cpuid_data.entries[cpuid_i++];
> -    c->function = KVM_CPUID_FEATURES | kvm_base;
> -    c->eax = env->features[FEAT_KVM];
> +        c = &cpuid_data.entries[cpuid_i++];
> +        c->function = KVM_CPUID_FEATURES | kvm_base;
> +        c->eax = env->features[FEAT_KVM];
>  
> -    has_msr_async_pf_en = c->eax & (1 << KVM_FEATURE_ASYNC_PF);
> +        has_msr_async_pf_en = c->eax & (1 << KVM_FEATURE_ASYNC_PF);
>  
> -    has_msr_pv_eoi_en = c->eax & (1 << KVM_FEATURE_PV_EOI);
> +        has_msr_pv_eoi_en = c->eax & (1 << KVM_FEATURE_PV_EOI);
>  
> -    has_msr_kvm_steal_time = c->eax & (1 << KVM_FEATURE_STEAL_TIME);
> +        has_msr_kvm_steal_time = c->eax & (1 << KVM_FEATURE_STEAL_TIME);
Does this mean that we don't expose these features if kvm=off is 
specified ?

> +    }
>  
>      cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);
>