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kvm: Add KVM_GET_EMULATED_CPUID

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Add a kvm ioctl which states which system functionality kvm emulates.
The format used is that of CPUID and we return the corresponding CPUID
bits set for which we do emulate functionality.

Make sure ->padding is being passed on clean from userspace so that we
can use it for something in the future, after the ioctl gets cast in
stone.

s/kvm_dev_ioctl_get_supported_cpuid/kvm_dev_ioctl_get_cpuid/ while at
it.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Borislav Petkov 2013-09-22 16:44:50 +02:00 • committed by Paolo Bonzini
parent 5bb3398dd2
commit 9c15bb1d0a
6 changed files with 139 additions and 17 deletions
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77
Documentation/virtual/kvm/api.txt
View file

@ -1122,9 +1122,9 @@ struct kvm_cpuid2 {
struct kvm_cpuid_entry2 entries[0];
};
#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX 1
#define KVM_CPUID_FLAG_STATEFUL_FUNC 2
#define KVM_CPUID_FLAG_STATE_READ_NEXT 4
#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX BIT(0)
#define KVM_CPUID_FLAG_STATEFUL_FUNC BIT(1)
#define KVM_CPUID_FLAG_STATE_READ_NEXT BIT(2)
struct kvm_cpuid_entry2 {
__u32 function;
@ -2684,6 +2684,77 @@ and usually define the validity of a groups of registers. (e.g. one bit
};
4.81 KVM_GET_EMULATED_CPUID
Capability: KVM_CAP_EXT_EMUL_CPUID
Architectures: x86
Type: system ioctl
Parameters: struct kvm_cpuid2 (in/out)
Returns: 0 on success, -1 on error
struct kvm_cpuid2 {
__u32 nent;
__u32 flags;
struct kvm_cpuid_entry2 entries[0];
};
The member 'flags' is used for passing flags from userspace.
#define KVM_CPUID_FLAG_SIGNIFCANT_INDEX BIT(0)
#define KVM_CPUID_FLAG_STATEFUL_FUNC BIT(1)
#define KVM_CPUID_FLAG_STATE_READ_NEXT BIT(2)
struct kvm_cpuid_entry2 {
__u32 function;
__u32 index;
__u32 flags;
__u32 eax;
__u32 ebx;
__u32 ecx;
__u32 edx;
__u32 padding[3];
};
This ioctl returns x86 cpuid features which are emulated by
kvm.Userspace can use the information returned by this ioctl to query
which features are emulated by kvm instead of being present natively.
Userspace invokes KVM_GET_EMULATED_CPUID by passing a kvm_cpuid2
structure with the 'nent' field indicating the number of entries in
the variable-size array 'entries'. If the number of entries is too low
to describe the cpu capabilities, an error (E2BIG) is returned. If the
number is too high, the 'nent' field is adjusted and an error (ENOMEM)
is returned. If the number is just right, the 'nent' field is adjusted
to the number of valid entries in the 'entries' array, which is then
filled.
The entries returned are the set CPUID bits of the respective features
which kvm emulates, as returned by the CPUID instruction, with unknown
or unsupported feature bits cleared.
Features like x2apic, for example, may not be present in the host cpu
but are exposed by kvm in KVM_GET_SUPPORTED_CPUID because they can be
emulated efficiently and thus not included here.
The fields in each entry are defined as follows:
function: the eax value used to obtain the entry
index: the ecx value used to obtain the entry (for entries that are
affected by ecx)
flags: an OR of zero or more of the following:
KVM_CPUID_FLAG_SIGNIFCANT_INDEX:
if the index field is valid
KVM_CPUID_FLAG_STATEFUL_FUNC:
if cpuid for this function returns different values for successive
invocations; there will be several entries with the same function,
all with this flag set
KVM_CPUID_FLAG_STATE_READ_NEXT:
for KVM_CPUID_FLAG_STATEFUL_FUNC entries, set if this entry is
the first entry to be read by a cpu
eax, ebx, ecx, edx: the values returned by the cpuid instruction for
this function/index combination
6. Capabilities that can be enabled
-----------------------------------