linux-kernel - Re: [PATCH 1/2] X86/KVM: Properly update 'tsc

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Date:   Fri, 13 Apr 2018 18:04:26 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH 1/2] X86/KVM: Properly update 'tsc_offset' to represent
 the running guest

On 13/04/2018 18:02, Jim Mattson wrote:
> On Fri, Apr 13, 2018 at 4:23 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>> From: KarimAllah Ahmed <karahmed@...zon.de>
>>
>> Update 'tsc_offset' on vmenty/vmexit of L2 guests to ensure that it always
>> captures the TSC_OFFSET of the running guest whether it is the L1 or L2
>> guest.
>>
>> Cc: Jim Mattson <jmattson@...gle.com>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Cc: kvm@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
>> Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
>> [AMD changes, fix update_ia32_tsc_adjust_msr. - Paolo]
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> 
>> @@ -11489,6 +11497,9 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>>         if (enable_shadow_vmcs)
>>                 copy_shadow_to_vmcs12(vmx);
>>
>> +       if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING)
>> +               vcpu->arch.tsc_offset += vmcs12->tsc_offset;
>> +
> 
> This seems a little early, since we don't restore the L1 TSC offset on
> the nested_vmx_failValid path.
> 

Now this can be a nice one to introduce the VMX API tests. :)  I'll try
to do it on Monday as punishment for not noticing the bug.  In the
meanwhile, Karim, can you post a fixed fixed version?

Paolo