Re: [Xen-devel] [PATCH v1 1/6] vmx: add struct vmx_msr_policy

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.07.17 at 11:21, <sergey.dyasli@xxxxxxxxxx> wrote:
> On Tue, 2017-07-04 at 07:57 -0600, Jan Beulich wrote:
>> > > > On 26.06.17 at 12:44, <sergey.dyasli@xxxxxxxxxx> wrote:
>> > 
>> > --- a/xen/include/asm-x86/hvm/vmx/vmcs.h
>> > +++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
>> > @@ -562,6 +562,350 @@ void vmx_domain_flush_pml_buffers(struct domain *d);
>> >  
>> >  void vmx_domain_update_eptp(struct domain *d);
>> >  
>> > +union vmx_pin_based_exec_control_bits {
>> > +    uint32_t raw;
>> > +    struct {
>> > +        bool ext_intr_exiting:1;
>> > +        uint32_t             :2;  /* 1:2 reserved */
>> > +        bool      nmi_exiting:1;
>> > +        uint32_t             :1;  /* 4 reserved */
>> > +        bool     virtual_nmis:1;
>> > +        bool    preempt_timer:1;
>> > +        bool posted_interrupt:1;
>> > +        uint32_t             :24; /* 8:31 reserved */
>> 
>> This mixture of bool and uint32_t worries me - I don't think the
>> resulting layout is well defined. Yes, you put suitable
>> BUILD_BUG_ON()s in place to catch possible issues, but anyway.
> 
> It was Andrew's suggestion to use bool because "It avoids subtle bugs like
> foo.exec_only = (a & EXEC) truncating to zero". In the end it doesn't matter
> which types are being used for bitfields, the layout depends only on the 
> width.

Okay, I've read the text again, and I now agree that using bool
ought to be fine.

Jan


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