Re: [PATCH RFC 2/6] x86/hyper-v: add a function to read both TSC and TSC page value simulateneously

[Vitaly Kuznetsov]

Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:

> On 01/12/2017 18:29, Stephen Hemminger wrote:
>>> +static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
>>> +				       u64 *cur_tsc)
>>> +{
>>> +	*cur_tsc = rdtsc();
>>> +
>>> +	return cur_tsc;
>> Why do return and setting by reference. Looks like an ugly API.
>
> This is the fallback implementation for !CONFIG_HYPERV_TSCPAGE, which
> explains why it's ugly, but why is it needed at all (or it could just
> BUG())?
>

It is not needed indeed, the intention was just to avoid '#if
IS_ENABLED(CONFIG_HYPERV)' in kvm code. I can replace it with BUG() or
return U64_MAX;

-- 
  Vitaly