[RFC PATCH v6 20/36] KVM: nVMX: Don't propagate vmcs12's PERF_GLOBAL_CTRL settings to vmcs02

Sean Christopherson
2022-08-24T03:04:27Z

Don't propagate vmcs12's VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL to vmcs02.
KVM doesn't disallow L1 from using VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL
even when KVM itself doesn't use the control, e.g. due to the various
CPU errata that where the MSR can be corrupted on VM-Exit.

Preserve KVM's (vmcs01) setting to hopefully avoid having to toggle the
bit in vmcs02 at a later point. E.g. if KVM is loading PERF_GLOBAL_CTRL
when running L1, then odds are good KVM will also load the MSR when
running L2.

Fixes: 8bf00a529967 ("KVM: VMX: add support for switching of PERF_GLOBAL_CTRL")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/nested.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 57e96f4ab765..eed7551dd63c 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2368,9 +2368,14 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
* are emulated by vmx_set_efer() in prepare_vmcs02(), but speculate
* on the related bits (if supported by the CPU) in the hope that
* we can avoid VMWrites during vmx_set_efer().
+ *
+ * Similarly, take vmcs01's PERF_GLOBAL_CTRL in the hope that if KVM is
+ * loading PERF_GLOBAL_CTRL via the VMCS for L1, then KVM will want to
+ * do the same for L2.
*/
exec_control = __vm_entry_controls_get(vmcs01);
- exec_control |= vmcs12->vm_entry_controls;
+ exec_control |= (vmcs12->vm_entry_controls &
+ ~VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL);
exec_control &= ~(VM_ENTRY_IA32E_MODE | VM_ENTRY_LOAD_IA32_EFER);
if (cpu_has_load_ia32_efer()) {
if (guest_efer & EFER_LMA)
--
2.37.1.595.g718a3a8f04-goog