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authorJing Liu <jing2.liu@intel.com>2022-01-05 15:35:15 +0300
committerPaolo Bonzini <pbonzini@redhat.com>2022-01-07 21:33:04 +0300
commit445ecdf79be0c71ca248f7611aeefceaea3ec59f (patch)
treede6de4d866343a9cddb7e1f0715e359f587eb211 /Documentation/virt
parentcc04b6a21d431359eceeec0d812b492088b04af5 (diff)
downloadlinux-445ecdf79be0c71ca248f7611aeefceaea3ec59f.tar.xz
kvm: x86: Exclude unpermitted xfeatures at KVM_GET_SUPPORTED_CPUID
KVM_GET_SUPPORTED_CPUID should not include any dynamic xstates in CPUID[0xD] if they have not been requested with prctl. Otherwise a process which directly passes KVM_GET_SUPPORTED_CPUID to KVM_SET_CPUID2 would now fail even if it doesn't intend to use a dynamically enabled feature. Userspace must know that prctl is required and allocate >4K xstate buffer before setting any dynamic bit. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Jing Liu <jing2.liu@intel.com> Signed-off-by: Yang Zhong <yang.zhong@intel.com> Message-Id: <20220105123532.12586-5-yang.zhong@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
-rw-r--r--Documentation/virt/kvm/api.rst4
1 files changed, 4 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 6b683dfea8f2..f4ea5e41a4d0 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -1687,6 +1687,10 @@ userspace capabilities, and with user requirements (for example, the
user may wish to constrain cpuid to emulate older hardware, or for
feature consistency across a cluster).
+Dynamically-enabled feature bits need to be requested with
+``arch_prctl()`` before calling this ioctl. Feature bits that have not
+been requested are excluded from the result.
+
Note that certain capabilities, such as KVM_CAP_X86_DISABLE_EXITS, may
expose cpuid features (e.g. MONITOR) which are not supported by kvm in
its default configuration. If userspace enables such capabilities, it