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

Xiaoyao Li
2024-04-01T07:07:23Z

On 3/16/2024 1:54 AM, Sean Christopherson wrote:
> 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.
>

+1.

However, it seems different for vmx_basic_vmcs_mem_type() in patch 5,
that I just recommended to define the MASK.

Because we already have

#define VMX_BASIC_MEM_TYPE_SHIFT 50

and it has been used in vmx/nested.c,

static inline u32 vmx_basic_vmcs_mem_type(u64 vmx_basic)
{
return (vmx_basic & GENMASK_ULL(53, 50)) >>
VMX_BASIC_MEM_TYPE_SHIFT;
}

looks not intuitive than original patch.