Re: [PATCH v2 1/3] KVM: x86: implement KVM_{GET|SET}_TSC_STATE

[Thomas Gleixner]

On Tue, Dec 08 2020 at 15:12, Marcelo Tosatti wrote:
> On Tue, Dec 08, 2020 at 06:25:13PM +0200, Maxim Levitsky wrote:
>> On Tue, 2020-12-08 at 17:02 +0100, Thomas Gleixner wrote:
>> The "bug" is that if VMM moves a hardware time counter (tsc or anything else) 
>> forward by large enough value in one go, 
>> then the guest kernel will supposingly have an overflow in the time code.
>> I don't consider this to be a buggy VMM behavior, but rather a kernel
>> bug that should be fixed (if this bug actually exists)
>
> It exists.

In the VMM. 

>> We are talking about the fact that TSC can jump forward by arbitrary large
>> value if the migration took arbitrary amount of time, which 
>> (assuming that the bug is real) can crash the guest kernel.
>
> QE reproduced it.

Sure, that's what QE is about. Just your conclusion is wrong.

Thanks,

        tglx