On 1/23/2023 9:00 PM, Sean Christopherson wrote:
> On Mon, Jan 23, 2023, Vitaly Kuznetsov wrote:
>> Alexandru Matei <alexandru.matei@xxxxxxxxxx> writes:
>>
>>> KVM enables 'Enlightened VMCS' and 'Enlightened MSR Bitmap' when running as
>>> a nested hypervisor on top of Hyper-V. When MSR bitmap is updated,
>>> evmcs_touch_msr_bitmap function uses current_vmcs per-cpu variable to mark
>>> that the msr bitmap was changed.
>
> ...
>
>>> @@ -219,7 +223,7 @@ static inline u64 evmcs_read64(unsigned long field) { return 0; }
>>> static inline u32 evmcs_read32(unsigned long field) { return 0; }
>>> static inline u16 evmcs_read16(unsigned long field) { return 0; }
>>> static inline void evmcs_load(u64 phys_addr) {}
>>> -static inline void evmcs_touch_msr_bitmap(void) {}
>>> +static inline void evmcs_touch_msr_bitmap(struct hv_enlightened_vmcs *evmcs) {}
>>> #endif /* IS_ENABLED(CONFIG_HYPERV) */
>>>
>>> #define EVMPTR_INVALID (-1ULL)
>>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>>> index fe5615fd8295..1d482a80bca8 100644
>>> --- a/arch/x86/kvm/vmx/vmx.c
>>> +++ b/arch/x86/kvm/vmx/vmx.c
>>> @@ -3869,7 +3869,7 @@ static void vmx_msr_bitmap_l01_changed(struct vcpu_vmx *vmx)
>>> * bitmap has changed.
>>> */
>>> if (static_branch_unlikely(&enable_evmcs))
>>> - evmcs_touch_msr_bitmap();
>>> + evmcs_touch_msr_bitmap((struct hv_enlightened_vmcs *)vmx->vmcs01.vmcs);
>>>
>>> vmx->nested.force_msr_bitmap_recalc = true;
>>> }
>>
>> Just in case we decide to follow this path and not merge
>> evmcs_touch_msr_bitmap() into vmx_msr_bitmap_l01_changed():
>
> This is the only approach that I'm outright opposed to. The evmcs_touch_msr_bitmap()
> stub is a lie in that it should never be reached with CONFIG_HYPERV=n, i.e. should
> really WARN. Ditto for the WARN_ON_ONCE() in the actual helper; if vmx->vmcs01.vmcs
> is NULL then KVM is completely hosed.
>
> KVM already consumes hv_enlightenments_control.msr_bitmap in vmx.c and in nested.c,
> shoving this case into hyperv.h but leaving those in VMX proper is odd/kludgy.
Got it, I'll send a v4 with your patch.
