From: Sean Christopherson <seanjc@google.com>
To: Makarand Sonare <makarandsonare@google.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
pbonzini@redhat.com, pshier@google.com, jmattson@google.com,
Ben Gardon <bgardon@google.com>
Subject: Re: [RESEND PATCH ] KVM: VMX: Enable/disable PML when dirty logging gets enabled/disabled
Date: Fri, 12 Feb 2021 14:13:05 -0800 [thread overview]
Message-ID: <YCb9cUwu+7SrM2sq@google.com> (raw)
In-Reply-To: <YCbws4v7Up2daHyQ@google.com>
On Fri, Feb 12, 2021, Sean Christopherson wrote:
> On Fri, Feb 12, 2021, Makarand Sonare wrote:
> > >> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > >> index 777177ea9a35e..eb6639f0ee7eb 100644
> > >> --- a/arch/x86/kvm/vmx/vmx.c
> > >> +++ b/arch/x86/kvm/vmx/vmx.c
> > >> @@ -4276,7 +4276,7 @@ static void
> > >> vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
> > >> */
> > >> exec_control &= ~SECONDARY_EXEC_SHADOW_VMCS;
> > >>
> > >> - if (!enable_pml)
> > >> + if (!enable_pml || !vcpu->kvm->arch.pml_enabled)
> > >> exec_control &= ~SECONDARY_EXEC_ENABLE_PML;
> > >
> > > The checks are unnecessary if PML is dynamically toggled, i.e. this
> > > snippet can unconditionally clear PML. When setting SECONDARY_EXEC
> > > (below snippet), PML will be preserved in the current controls, which is
> > > what we want.
> >
> > Assuming a new VCPU can be added at a later time after PML is already
> > enabled, should we clear
> > PML in VMCS for the new VCPU. If yes what will be the trigger for
> > setting PML for the new VCPU?
>
> Ah, didn't consider that. Phooey.
I remember why I thought this could be unconditional. Adding PML to the list of
dynamic bits in vmcs_set_secondary_exec_control() effectively makes this code
unconditional, because it means that current bit will be preserved, including
the case where PML=0 when a vCPU is created.
I believe the fix is simply to not mark PML as fully dynamic.
prev parent reply other threads:[~2021-02-12 22:13 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-10 21:23 [RESEND PATCH ] KVM: VMX: Enable/disable PML when dirty logging gets enabled/disabled Makarand Sonare
2021-02-11 0:55 ` Sean Christopherson
2021-02-11 9:04 ` Paolo Bonzini
2021-02-11 18:20 ` Sean Christopherson
2021-02-11 2:07 ` Sean Christopherson
2021-02-11 8:58 ` Paolo Bonzini
2021-02-11 9:04 ` Paolo Bonzini
2021-02-11 15:53 ` Sean Christopherson
2021-02-12 18:12 ` Sean Christopherson
2021-02-12 19:14 ` Makarand Sonare
2021-02-12 21:18 ` Sean Christopherson
2021-02-12 22:13 ` Sean Christopherson [this message]
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