> On 18 Jun 2019, at 18:48, Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> wrote:
>
> * Liran Alon (liran.alon@xxxxxxxxxx) wrote:
>>
>>> On 18 Jun 2019, at 12:03, Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> wrote:
>>>
>>> * Liran Alon (liran.alon@xxxxxxxxxx) wrote:
>>>>
>>>> +static const VMStateDescription vmstate_vmx_vmcs12 = {
>>>> + .name = "cpu/kvm_nested_state/vmx/vmcs12",
>>>> + .version_id = 1,
>>>> + .minimum_version_id = 1,
>>>> + .needed = vmx_vmcs12_needed,
>>>> + .fields = (VMStateField[]) {
>>>> + VMSTATE_UINT8_ARRAY(data.vmx[0].vmcs12,
>>>> + struct kvm_nested_state, 0x1000),
>>>
>>> Where did that magic 0x1000 come from?
>>
>> Currently, KVM folks (including myself), haven’t decided yet to expose vmcs12 struct layout to userspace but instead to still leave it opaque.
>> The formal size of this size is VMCS12_SIZE (defined in kernel as 0x1000). I was wondering if we wish to expose VMCS12_SIZE constant to userspace or not.
>> So currently I defined these __u8 arrays as 0x1000. But in case Paolo agrees to expose VMCS12_SIZE, we can use that instead.
>
> Well if it's not defined it's bound to change at some state!
I agree it’s better to expose VMCS12_SIZE to userspace but I didn’t want to be the one that decides this.
Let’s let Paolo decide and modify this patch accordingly if he decides to expose it.
> Also, do we need to clear it before we get it from the kernel - e.g.
> is the kernel guaranteed to give us 0x1000 ?
Userspace don’t need to clear it before getting it from kernel.
It does guarantee to give you 0x1000. See vmx_get_nested_state() implementation in kernel.
-Liran
>
> Dave
>
>> -Liran
>>
>>> --
>>> Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
>>
> --
> Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
