On Fri, May 30, 2014 at 4:49 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> Il 20/05/2014 04:25, Jidong Xiao ha scritto:
>
>> Hi,
>>
>> The structure kvm_segment is defined as follows:
>>
>> struct kvm_segment {
>> __u64 base;
>> __u32 limit;
>> __u16 selector;
>> __u8 type;
>> __u8 present, dpl, db, s, l, g, avl;
>> __u8 unusable;
>> __u8 padding;
>> };
>>
>> Since the VMX spec defines base is 64 bits, limit is 32bits, selector
>> is 16bits, understandably, __u64, __u32, __u16 is used for them
>> respectively.
>>
>> However, the VMX spec defines that the access rights is 32bits, which
>> includes a 4 bits type, 2 bits dpl, and 1 bit for the
>> present,dpl,db,s,l,g,avl. So why here they are all defined as __u8? It
>> means that, each of them is represented by 8bits? This looks
>> inconsistent with the VMX spec.
>
>
> This is not a VMX definition, it's part of the ioctl interface between KVM
> and user-mode programs.
>
> For the conversion code see vmx_get_segment and vmx_set_segment. These
> should be never called in hot paths, except unfortunately when doing nested
> virtualization.
>
> Paolo
Thanks Paolo. I will try to read the source code and intel manual and
try to understand what you explained.
-Jidong
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