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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com,
	jmattson@google.com
Subject: Re: [PATCH 4/8][KVM nVMX]: Check "load IA32_PERF_GLOBAL_CTRL" VM-exit control on vmentry of nested guests
Date: Fri, 17 May 2019 13:34:40 -0700
Message-ID: <20190517203440.GL15006@linux.intel.com> (raw)
In-Reply-To: <2c08cd38-fd7d-da68-7c8d-2c7c93c3a9c8@oracle.com>

On Thu, May 16, 2019 at 03:07:48PM -0700, Krish Sadhukhan wrote:
> 
> 
> On 05/13/2019 12:00 PM, Sean Christopherson wrote:
> >On Wed, Apr 24, 2019 at 07:17:20PM -0400, Krish Sadhukhan wrote:
> >>According to section "Checks on Host Control Registers and MSRs" in Intel
> >>SDM vol 3C, the following check is performed on vmentry of nested guests:
> >>
> >>     "If the "load IA32_PERF_GLOBAL_CTRL" VM-exit control is 1, bits reserved
> >>     in the IA32_PERF_GLOBAL_CTRL MSR must be 0 in the field for that
> >>     register."
> >>
> >>Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> >>Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
> >>---
> >>  arch/x86/kvm/vmx/nested.c | 5 +++++
> >>  1 file changed, 5 insertions(+)
> >>
> >>diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> >>index 83cd887638cb..d2067370e288 100644
> >>--- a/arch/x86/kvm/vmx/nested.c
> >>+++ b/arch/x86/kvm/vmx/nested.c
> >>@@ -2595,6 +2595,11 @@ static int nested_check_host_control_regs(struct kvm_vcpu *vcpu,
> >>  	    !nested_host_cr4_valid(vcpu, vmcs12->host_cr4) ||
> >>  	    !nested_cr3_valid(vcpu, vmcs12->host_cr3))
> >>  		return -EINVAL;
> >>+
> >>+	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL &&
> >>+	   !kvm_valid_perf_global_ctrl(vmcs12->host_ia32_perf_global_ctrl))
> >If vmcs12->host_ia32_perf_global_ctrl were ever actually consumed, this
> >needs to ensure L1 isn't able to take control of counters that are owned
> >by the host.
> 
> Sorry, I didn't understand your concern. Could you please explain how L1 can
> control L0's counters ?

MSR_CORE_PERF_GLOBAL_CTRL isn't virtualized in the sense that there is
only one MSR in hardware (per logical CPU).  Loading an arbitrary value
into hardware on a nested VM-Exit via vmcs12->host_ia32_perf_global_ctrl
means L1 could toggle counters on/off without L0's knowledge.  See
intel_guest_get_msrs() and intel_pmu_set_msr().

Except that your patches don't actually do anything functional with
vmcs12->host_ia32_perf_global_ctrl, hence my confusion over what you're
trying to accomplish.  If KVM advertises VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL
to L1, then L1 will think it can use the VMCS field to handle
MSR_CORE_PERF_GLOBAL_CTRL when running L2, e.g. instead of adding
MSR_CORE_PERF_GLOBAL_CTRL to the MSR load lists, which will break L1
(assuming nested PMU works today).

  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 [this message]
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
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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