Re: [PATCH v2 0/1] x86/kvm/hyper-v: Add support to SYNIC exit on EOM

[Jon Doron <arilou@gmail.com>]

On 05/05/2020, Roman Kagan wrote:
>On Tue, May 05, 2020 at 01:38:21PM +0300, Jon Doron wrote:
>> On 05/05/2020, Roman Kagan wrote:
>> > On Mon, May 04, 2020 at 05:55:10PM +0200, Vitaly Kuznetsov wrote:
>> > > and it seems the default state of HV_X64_MSR_SCONTROL is '1', we should
>> > > probably do the same.
>> >
>> > This is the state the OS sees, after the firmware.  You'd see the same
>> > with QEMU/KVM if you used Hyper-V-aware SeaBIOS or OVMF.
>> >
>> > > Is there any reason to *not* do this in KVM when
>> > > KVM_CAP_HYPERV_SYNIC[,2] is enabled?
>> >
>> > Yes there is: quoting Hyper-V TLFS v6.0 11.8.1:
>> >
>> >  At virtual processor creation time and upon processor reset, the value
>> >  of this SCONTROL (SynIC control register) is 0x0000000000000000. Thus,
>> >  message queuing and event flag notifications will be disabled.
>> >
>> > And, even if we decide to violate the spec it's better done in
>> > userspace, loading the initial value and adjusting the synic state at
>> > vcpu reset.
>> >
>> > However leaving it up to the guest (firmware or OS) looks more natural
>> > to me.
>>
>> I under where you are coming from in the idea of leaving it to the OS
>
>I'm coming from the HyperV spec, see the quote above.
>
>> but I think in this specific case it does not make much sense, after
>> all HyperV has it's own proprietary BIOS which Windows assumes has
>> setup some of the MSRs, since we dont have that BIOS we need to
>> "emulate" it's behaviour.
>
>We don't have that BIOS, but we have another BIOS which does the same
>and is not proprietary.  Using it allows to do synic message posting
>even with a non-compliant guest OS which doesn't properly enable
>SCONTROL on its own.  (Note that there used to be no problem with this
>so far, this must be specific to your use case.)
>
>I'm failing to see why this is a stumbling block for the work you're
>doing.
>
>And I'm not convinced we need to work around a non-compliant guest with
>kludges to KVM or QEMU (including back-compat stuff as that would change
>the existing behavior), when the desired effect can be achieved with the
>existing code.
>
>Thanks,
>Roman.

Thanks Roman, I see your point, it's important for me to get the EDK2 
working properly not sure why it's not working for me.

Do you know by any chance if the EDK2 hyperv patches were submitted and 
if they were why they were not merged in?

Thanks,
-- Jon.