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From: Jim Mattson <jmattson@google.com>
To: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Cc: "kvm list" <kvm@vger.kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH 6/8][KVM nVMX]: Load IA32_PERF_GLOBAL_CTRL MSR on vmentry of nested guests
Date: Fri, 23 Aug 2019 08:57:38 -0700
Message-ID: <CALMp9eRCE22HACZZ_=3nZgpx7MbSBWPEJdMXZchp7EB3K-hkVg@mail.gmail.com> (raw)
In-Reply-To: <a2889868-eb62-5843-f3d2-fe066055e80c@oracle.com>

On Thu, Aug 22, 2019 at 10:29 PM Krish Sadhukhan
<krish.sadhukhan@oracle.com> wrote:
>
>
> On 8/15/19 3:44 PM, Jim Mattson wrote:
> > On Wed, Apr 24, 2019 at 4:43 PM Krish Sadhukhan
> > <krish.sadhukhan@oracle.com> wrote:
> >> According to section "Loading Guest State" in Intel SDM vol 3C, the
> >> IA32_PERF_GLOBAL_CTRL MSR is loaded on vmentry of nested guests:
> >>
> >>      "If the “load IA32_PERF_GLOBAL_CTRL” VM-entry control is 1, the
> >>       IA32_PERF_GLOBAL_CTRL MSR is loaded from the IA32_PERF_GLOBAL_CTRL
> >>       field."
> >>
> >> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> >> Suggested-by: Jim Mattson <jmattson@google.com>
> >> Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
> >> ---
> >>   arch/x86/kvm/vmx/nested.c | 4 ++++
> >>   1 file changed, 4 insertions(+)
> >>
> >> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> >> index a7bf19eaa70b..8177374886a9 100644
> >> --- a/arch/x86/kvm/vmx/nested.c
> >> +++ b/arch/x86/kvm/vmx/nested.c
> >> @@ -2300,6 +2300,10 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
> >>          vcpu->arch.cr0_guest_owned_bits &= ~vmcs12->cr0_guest_host_mask;
> >>          vmcs_writel(CR0_GUEST_HOST_MASK, ~vcpu->arch.cr0_guest_owned_bits);
> >>
> >> +       if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
> >> +               vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL,
> >> +                            vmcs12->guest_ia32_perf_global_ctrl);
> >> +
> >>          if (vmx->nested.nested_run_pending &&
> >>              (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PAT)) {
> >>                  vmcs_write64(GUEST_IA32_PAT, vmcs12->guest_ia32_pat);
> >> --
> >> 2.17.2
> >>
> > This isn't quite right. The GUEST_IA32_PERF_GLOBAL_CTRL value is just
> > going to get overwritten later by atomic_switch_perf_msrs().
> >
> > Instead of writing the vmcs12 value directly into the vmcs02, you
> > should call kvm_set_msr(), exactly as it would have been called if
> > MSR_CORE_PERF_GLOBAL_CTRL had been in the vmcs12
> > VM-entry MSR-load list. Then, atomic_switch_perf_msrs() will
> > automatically do the right thing.
>
>
> I notice that the existing code for VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL
> in load_vmcs12_host_state() doesn't use kvm_set_msr():
>
>              if (vmcs12->vm_exit_controls &
> VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL)
>                  vmcs_write64(GUEST_IA32_PERF_GLOBAL_CTRL,
>                          vmcs12->host_ia32_perf_global_ctrl);
>
> This should also be changed to use kvm_set_msr() then ?

Yes. The VMWRITE here is incorrect, but fortunately it is also unreachable.

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-24 23:17 [KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" " Krish Sadhukhan
2019-04-24 23:17 ` [PATCH 1/8][KVMnVMX]: Enable "load IA32_PERF_GLOBAL_CTRL" VM-exit control for " Krish Sadhukhan
2019-05-13 18:49   ` Sean Christopherson
2019-05-13 22:08     ` Krish Sadhukhan
2019-04-24 23:17 ` [PATCH 2/8][KVM nVMX]: Enable "load IA32_PERF_GLOBAL_CTRL" VM-entry " Krish Sadhukhan
2019-05-13 18:49   ` Sean Christopherson
2019-04-24 23:17 ` [PATCH 3/8][KVM VMX]: Add a function to check reserved bits in MSR_CORE_PERF_GLOBAL_CTRL Krish Sadhukhan
2019-05-13 18:57   ` Sean Christopherson
2019-08-15 22:29     ` Jim Mattson
2019-04-24 23:17 ` [PATCH 4/8][KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" VM-exit control on vmentry of nested guests Krish Sadhukhan
2019-05-13 19:00   ` Sean Christopherson
2019-05-16 22:07     ` Krish Sadhukhan
2019-05-17 20:34       ` Sean Christopherson
2019-08-15 22:54         ` Jim Mattson
2019-04-24 23:17 ` [PATCH 5/8][KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" VM-entry " Krish Sadhukhan
2019-08-15 22:36   ` Jim Mattson
2019-04-24 23:17 ` [PATCH 6/8][KVM nVMX]: Load IA32_PERF_GLOBAL_CTRL MSR " Krish Sadhukhan
2019-08-15 22:44   ` Jim Mattson
2019-08-21 23:05     ` Krish Sadhukhan
2019-08-21 23:10       ` Jim Mattson
2019-08-23  5:29     ` Krish Sadhukhan
2019-08-23 15:57       ` Jim Mattson [this message]
2019-04-24 23:17 ` [PATCH 7/8][KVM nVMX]: Enable "load IA32_PERF_GLOBAL_CTRL VM-{entry,exit} controls Krish Sadhukhan
2019-05-13 19:12   ` Sean Christopherson
2019-08-15 23:02     ` Jim Mattson
2019-04-24 23:17 ` [PATCH 8/8][KVM nVMX]: Test "load IA32_PERF_GLOBAL_CTRL" controls on vmentry of nested guests Krish Sadhukhan
2019-05-13 18:46 ` [KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" " Sean Christopherson

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