Re: [PATCH v6 8/9] KVM: VMX: Open code VMX preemption timer rate mask in its accessor

Sean Christopherson
2024-03-15T17:54:17Z

On Fri, Mar 15, 2024, Zhao Liu wrote:
> On Fri, Mar 08, 2024 at 05:27:24PM -0800, Sean Christopherson wrote:
> > Use vmx_misc_preemption_timer_rate() to get the rate in hardware_setup(),
> > and open code the rate's bitmask in vmx_misc_preemption_timer_rate() so
> > that the function looks like all the helpers that grab values from
> > VMX_BASIC and VMX_MISC MSR values.

...

> > -#define VMX_MISC_PREEMPTION_TIMER_RATE_MASK GENMASK_ULL(4, 0)
> > #define VMX_MISC_SAVE_EFER_LMA BIT_ULL(5)
> > #define VMX_MISC_ACTIVITY_HLT BIT_ULL(6)
> > #define VMX_MISC_ACTIVITY_SHUTDOWN BIT_ULL(7)
> > @@ -162,7 +161,7 @@ static inline u32 vmx_basic_vmcs_mem_type(u64 vmx_basic)
> >
> > static inline int vmx_misc_preemption_timer_rate(u64 vmx_misc)
> > {
> > - return vmx_misc & VMX_MISC_PREEMPTION_TIMER_RATE_MASK;
> > + return vmx_misc & GENMASK_ULL(4, 0);
> > }
>
> I feel keeping VMX_MISC_PREEMPTION_TIMER_RATE_MASK is clearer than
> GENMASK_ULL(4, 0), and the former improves code readability.
>
> May not need to drop VMX_MISC_PREEMPTION_TIMER_RATE_MASK?

I don't necessarily disagree, but in this case I value consistency over one
individual case. As called out in the changelog, the motivation is to make
vmx_misc_preemption_timer_rate() look like all the surrounding helpers.

_If_ we want to preserve the mask, then we should add #defines for vmx_misc_cr3_count(),
vmx_misc_max_msr(), etc.

I don't have a super strong preference, though I think my vote would be to not
add the masks and go with this patch. These helpers are intended to be the _only_
way to access the fields, i.e. they effectively _are_ the mask macros, just in
function form.