Re: [PATCH v2 4/7] KVM: SVM: hyper-v: Nested enlightenments in VMCB

[Vineeth Pillai]

On 4/16/2021 4:58 AM, Vitaly Kuznetsov wrote:
> > +
> > +#if IS_ENABLED(CONFIG_HYPERV)
> > +struct __packed hv_enlightenments {
> > +	struct __packed hv_enlightenments_control {
> > +		u32 nested_flush_hypercall:1;
> > +		u32 msr_bitmap:1;
> > +		u32 enlightened_npt_tlb: 1;
> > +		u32 reserved:29;
> > +	} hv_enlightenments_control;
> > +	u32 hv_vp_id;
> > +	u64 hv_vm_id;
> > +	u64 partition_assist_page;
> > +	u64 reserved;
> > +};
> Enlightened VMCS seems to have the same part:
>
>          struct {
>                  u32 nested_flush_hypercall:1;
>                  u32 msr_bitmap:1;
>                  u32 reserved:30;
>          }  __packed hv_enlightenments_control;
>          u32 hv_vp_id;
>          u64 hv_vm_id;
>          u64 partition_assist_page;
>
> Would it maybe make sense to unify these two (in case they are the same
> thing in Hyper-V, of course)?
They are very similar but,  the individual bits are a bit different. SVM 
struct has an
additional bit 'enlightened_npt_tlb'. There might be future changes as 
well if new
enlightenments are designed for performance optimization. So I feel, we 
can have
it as separate structs.


> >   
> > +#define VMCB_ALL_CLEAN_MASK (					\
> > +	(1U << VMCB_INTERCEPTS) | (1U << VMCB_PERM_MAP) |	\
> > +	(1U << VMCB_ASID) | (1U << VMCB_INTR) |			\
> > +	(1U << VMCB_NPT) | (1U << VMCB_CR) | (1U << VMCB_DR) |	\
> > +	(1U << VMCB_DT) | (1U << VMCB_SEG) | (1U << VMCB_CR2) |	\
> > +	(1U << VMCB_LBR) | (1U << VMCB_AVIC)			\
> > +	)
> What if we preserve VMCB_DIRTY_MAX and drop this newly introduced
> VMCB_ALL_CLEAN_MASK (which basically lists all the members of the enum
> above)? '1 << VMCB_DIRTY_MAX' can still work. (If the 'VMCB_DIRTY_MAX'
> name becomes misleading we can e.g. rename it to VMCB_NATIVE_DIRTY_MAX
> or something but I'm not sure it's worth it)

I thought of keeping this code because, if we have non-contiguous bits 
in future, we
would need this kinda logic anyways. But I get your point. Will revert this.


> > +#if IS_ENABLED(CONFIG_HYPERV)
> > +#define VMCB_HYPERV_CLEAN_MASK (1U << VMCB_HV_NESTED_ENLIGHTENMENTS)
> > +#endif
> VMCB_HYPERV_CLEAN_MASK is a single bit, why do we need it at all
> (BIT(VMCB_HV_NESTED_ENLIGHTENMENTS) is not super long)

Agreed. Will change it in next revision.

Thanks,
Vineeth