Re: [Xen-devel] [PATCH 03/13] x86/hvm: Collect information of TSC scaling ratio

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On Thu, Oct 22, 2015 at 08:51:13AM -0600, Jan Beulich wrote:
> >>> On 22.10.15 at 16:40, <haozhong.zhang@xxxxxxxxx> wrote:
> > On Thu, Oct 22, 2015 at 06:53:27AM -0600, Jan Beulich wrote:
> >> >>> On 28.09.15 at 09:13, <haozhong.zhang@xxxxxxxxx> wrote:
> >> > --- a/xen/include/asm-x86/hvm/svm/svm.h
> >> > +++ b/xen/include/asm-x86/hvm/svm/svm.h
> >> > @@ -96,6 +96,7 @@ extern u32 svm_feature_flags;
> >> >  
> >> >  /* TSC rate */
> >> >  #define DEFAULT_TSC_RATIO       0x0000000100000000ULL
> >> > +#define MAX_TSC_RATIO           0x000000ffffffffffULL
> >> >  #define TSC_RATIO_RSVD_BITS     0xffffff0000000000ULL
> >> 
> >> How about 
> >> 
> >> #define MAX_TSC_RATIO           (~TSC_RATIO_RSVD_BITS)
> > 
> > Yes.
> > 
> >> ? (But of course it's not really clear in which way this is to
> >> be used as "maximum" without seeing the code using it. I.e.
> >> it's not clear whether you don't really just mean to specify
> >> all the valid bits in the MSR.)
> > 
> > The reserved bits are used to calculate the maximum TSC ratio which is
> > used in hvm_setup_tsc_scaling() in patch 4 to check the whether a TSC
> > scaling ratio is legal.
> 
> The main motivation behind the comment was to understand
> whether one of the two constants wouldn't suffice.
>

Yes, either one itself is suffice. I'll only use the max ratio in the
next version (especially that VMX TSC scaling does not reserve any bits)

> Jan
> 

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