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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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