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i386: Support KVM_CAP_HYPERV_ENFORCE_CPUID

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By default, KVM allows the guest to use all currently supported Hyper-V
enlightenments when Hyper-V CPUID interface was exposed, regardless of if
some features were not announced in guest visible CPUIDs. hv-enforce-cpuid
feature alters this behavior and only allows the guest to use exposed
Hyper-V enlightenments. The feature is supported by Linux >= 5.14 and is
not enabled by default in QEMU.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210902093530.345756-5-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2021-09-02 11:35:26 +02:00 committed by Paolo Bonzini
parent 988f7b8bfe
commit 70367f0917
4 changed files with 25 additions and 3 deletions
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17
docs/hyperv.txt
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@ -203,8 +203,11 @@ When the option is set to 'on' QEMU will always enable the feature, regardless
of host setup. To keep guests secure, this can only be used in conjunction with of host setup. To keep guests secure, this can only be used in conjunction with
exposing correct vCPU topology and vCPU pinning. exposing correct vCPU topology and vCPU pinning.
4. Development features 4. Supplementary features
======================== =========================
4.1. hv-passthrough
===================
In some cases (e.g. during development) it may make sense to use QEMU in In some cases (e.g. during development) it may make sense to use QEMU in
'pass-through' mode and give Windows guests all enlightenments currently 'pass-through' mode and give Windows guests all enlightenments currently
supported by KVM. This pass-through mode is enabled by "hv-passthrough" CPU supported by KVM. This pass-through mode is enabled by "hv-passthrough" CPU
@ -215,8 +218,16 @@ values from KVM to QEMU. "hv-passthrough" overrides all other "hv-*" settings on
the command line. Also, enabling this flag effectively prevents migration as the the command line. Also, enabling this flag effectively prevents migration as the
list of enabled enlightenments may differ between target and destination hosts. list of enabled enlightenments may differ between target and destination hosts.
4.2. hv-enforce-cpuid
=====================
By default, KVM allows the guest to use all currently supported Hyper-V
enlightenments when Hyper-V CPUID interface was exposed, regardless of if
some features were not announced in guest visible CPUIDs. 'hv-enforce-cpuid'
feature alters this behavior and only allows the guest to use exposed Hyper-V
enlightenments.
4. Useful links
5. Useful links
================ ================
Hyper-V Top Level Functional specification and other information: Hyper-V Top Level Functional specification and other information:
https://github.com/MicrosoftDocs/Virtualization-Documentation https://github.com/MicrosoftDocs/Virtualization-Documentation

1
target/i386/cpu.c
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@ -6834,6 +6834,7 @@ static Property x86_cpu_properties[] = {
DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU, DEFINE_PROP_ON_OFF_AUTO("hv-no-nonarch-coresharing", X86CPU,
hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF), hyperv_no_nonarch_cs, ON_OFF_AUTO_OFF),
DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false), DEFINE_PROP_BOOL("hv-passthrough", X86CPU, hyperv_passthrough, false),
DEFINE_PROP_BOOL("hv-enforce-cpuid", X86CPU, hyperv_enforce_cpuid, false),
DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, true), DEFINE_PROP_BOOL("check", X86CPU, check_cpuid, true),
DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false), DEFINE_PROP_BOOL("enforce", X86CPU, enforce_cpuid, false),

1
target/i386/cpu.h
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@ -1719,6 +1719,7 @@ struct X86CPU {
uint32_t hyperv_version_id[4]; uint32_t hyperv_version_id[4];
uint32_t hyperv_limits[3]; uint32_t hyperv_limits[3];
uint32_t hyperv_nested[4]; uint32_t hyperv_nested[4];
bool hyperv_enforce_cpuid;
bool check_cpuid; bool check_cpuid;
bool enforce_cpuid; bool enforce_cpuid;

9
target/i386/kvm/kvm.c
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@ -1531,6 +1531,15 @@ static int hyperv_init_vcpu(X86CPU *cpu)
cpu->hyperv_nested[0] = evmcs_version; cpu->hyperv_nested[0] = evmcs_version;
} }
if (cpu->hyperv_enforce_cpuid) {
ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENFORCE_CPUID, 0, 1);
if (ret < 0) {
error_report("failed to enable KVM_CAP_HYPERV_ENFORCE_CPUID: %s",
strerror(-ret));
return ret;
}
}
return 0; return 0;
} }