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

Vineeth Pillai
2021-04-16T17:07:15Z

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