On Tue, Apr 02, 2024, Sean Christopherson wrote:
> On Mon, Apr 01, 2024, Xiaoyao Li wrote:
> > 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.
>
> Yeah, agreed, that's taking the worst of both worlds. I'll update patch 5 to drop
> VMX_BASIC_MEM_TYPE_SHIFT when effectively "moving" it into vmx_basic_vmcs_mem_type().
Drat. Finally getting back to this, dropping VMX_BASIC_MEM_TYPE_SHIFT doesn't
work because it's used by nested_vmx_setup_basic(), as is VMX_BASIC_VMCS_SIZE_SHIFT,
which is presumably why past me kept them around.
I'm leaning towards keeping things as proposed in this series. I don't see us
gaining a third copy, or even a third user, i.e. I don't think we are creating a
future problem by open coding the shift in vmx_basic_vmcs_mem_type(). And IMO
code like this
return (vmx_basic & VMX_BASIC_MEM_TYPE_MASK) >>
VMX_BASIC_MEM_TYPE_SHIFT;
is an unnecessary obfuscation when there is literally one user (the accessor).
Another idea would be to delete VMX_BASIC_MEM_TYPE_SHIFT and VMX_BASIC_VMCS_SIZE_SHIFT,
and either open code the values or use local const variables, but that also seems
like a net negative, e.g. splits the effective definitions over too many locations.
