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

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Date:   Sat, 14 Apr 2018 03:11:18 +0000
From:   "Raslan, KarimAllah" <karahmed@...zon.de>
To:     "jmattson@...gle.com" <jmattson@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH 1/2] X86/KVM: Properly update 'tsc_offset' to represent
 the running guest

On Fri, 2018-04-13 at 18:04 +0200, Paolo Bonzini wrote:
> 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?

done

> 
> Paolo
> 
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