Re: [Xen-devel] [PATCH v2] x86/monitor: add support for descriptor access events

[Adrian Pop <apop@xxxxxxxxxxxxxxx>]

On Thu, Apr 06, 2017 at 03:20:21AM -0600, Jan Beulich wrote:
> >>> On 06.04.17 at 10:59, <apop@xxxxxxxxxxxxxxx> wrote:
> > On Wed, Apr 05, 2017 at 08:26:27AM -0600, Jan Beulich wrote:
> >> >>> On 04.04.17 at 11:57, <apop@xxxxxxxxxxxxxxx> wrote:
> >> > --- a/xen/arch/x86/hvm/hvm.c
> >> > +++ b/xen/arch/x86/hvm/hvm.c
> >> > @@ -3572,6 +3572,43 @@ gp_fault:
> >> >      return X86EMUL_EXCEPTION;
> >> >  }
> >> >  
> >> > +int hvm_descriptor_access_intercept(uint64_t exit_info,
> >> > +                                    uint64_t vmx_exit_qualification,
> >> > +                                    uint8_t descriptor, bool is_write)
> >> 
> >> Why uint8_t?
> > 
> > The descriptor type from struct vm_event_desc_access is uint8_t since
> > there are only 4 possible descriptors:
> > 
> >> > +#define VM_EVENT_DESC_IDTR           1
> >> > +#define VM_EVENT_DESC_GDTR           2
> >> > +#define VM_EVENT_DESC_LDTR           3
> >> > +#define VM_EVENT_DESC_TR             4
> > 
> > Should it be something else?
> 
> Well, you should avoid fixed width types where they're not really
> needed (their use should signal a true dependency on the specified
> width). "unsigned int" would be quite fine here afaict.

So should it be changed in the struct definition as well?

> >> > +struct vm_event_desc_access {
> >> > +    union {
> >> > +        struct {
> >> > +            uint32_t instr_info;         /* VMX: VMCS 
> >> > Instruction-Information */
> >> > +            uint32_t _pad1;
> >> > +            uint64_t exit_qualification; /* VMX: VMCS Exit 
> >> > Qualification */
> >> > +        } vmx;
> >> > +        struct {
> >> > +            uint64_t exitinfo;           /* SVM: VMCB EXITINFO */
> >> > +            uint64_t _pad2;
> >> > +        } svm;
> >> > +    } arch;
> >> > +    uint8_t descriptor;                  /* VM_EVENT_DESC_* */
> >> > +    uint8_t is_write;
> >> > +    uint8_t _pad[6];
> >> > +};

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