From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wanpeng Li <kernellwp@gmail.com>
Subject: Re: [PATCH] KVM: x86: pvclock: Handle first-time write to
 pvclock-page contains random junk
Date: Mon, 13 Nov 2017 09:37:59 +0800
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2017-11-13 9:03 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 2017-11-13 8:55 GMT+08:00 Liran Alon <LIRAN.ALON@oracle.com>:
>>
>>
>> On 13/11/17 02:52, Wanpeng Li wrote:
>>>
>>> 2017-11-13 8:44 GMT+08:00 Liran Alon <LIRAN.ALON@oracle.com>:
>>>>
>>>>
>>>>
>>>> On 13/11/17 02:40, Wanpeng Li wrote:
>>>>>
>>>>>
>>>>> 2017-11-05 22:11 GMT+08:00 Liran Alon <liran.alon@oracle.com>:
>>>>>>
>>>>>>
>>>>>> When guest passes KVM it's pvclock-page GPA via WRMSR to
>>>>>> MSR_KVM_SYSTEM_TIME / MSR_KVM_SYSTEM_TIME_NEW, KVM don't initialize
>>>>>> pvclock-page to some start-values. It just requests a clock-update
>>>>>> which
>>>>>
>>>>>
>>>>>
>>>>> KVM does, please refer to memset(hv_clock, 0, size) in kvmclock_init().
>>>>
>>>>
>>>>
>>>> kvmclock_init() is the code that runs in KVM-guest. I was talking here
>>>> about
>>>> the code that handles the WRMSR in KVM hypervisor code.
>>>>
>>>> The issue happens when the guest doesn't init pvclock-page as done in
>>>> kvmclock_init(). Not all guests behave nicely :)
>>>
>>>
>>> But the codes which you modify just works for kvm guest I think.
>>
>> No, it's the code that runs in KVM hypervisor for any guest that knows how
>> to work with KVM pv-clock PV interface.
>> Linux guest is just one of the possible guests which can use this interface.
>> kvmclock_init() you mentioned is part of the linux-guest. But there are
>> other guests which use KVM pv-clock PV interface.
>
> Good to know it, could you point one?

In addition, there is a BUG_ON(if version != 0) just before the codes
which you added. I will move these avoid random junk logics into msr
setup in order that it can avoid '& operation' each time update the pv
stuff. I will send a patch later.

Regards,
Wanpeng Li