diff mbox series

[v1,06/23] KVM: VMX: Defer enabling FRED MSRs save/load until after set CPUID

Message ID 20231108183003.5981-7-xin3.li@intel.com
State New
Headers show
Series Enable FRED with KVM VMX | expand

Commit Message

Li, Xin3 Nov. 8, 2023, 6:29 p.m. UTC 
Clear FRED VM entry/exit controls when initializing a vCPU, and set
these controls only if FRED is enumerated after set CPUID.

FRED VM entry/exit controls need to be set to establish context
sufficient to support FRED event delivery immediately after VM entry
and exit.  However it is not required to save/load FRED MSRs for
a non-FRED guest, which aren't supposed to access FRED MSRs.

A non-FRED guest should get #GP upon accessing FRED MSRs, otherwise
it corrupts host FRED MSRs.

Tested-by: Shan Kang <shan.kang@intel.com>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
 arch/x86/kvm/vmx/vmx.c | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

Comments

Li, Xin3 Nov. 9, 2023, 11:50 p.m. UTC | #1 
> >+static void vmx_vcpu_config_fred_after_set_cpuid(struct kvm_vcpu *vcpu)
> >+{
> >+	struct vcpu_vmx *vmx = to_vmx(vcpu);
> >+
> >+	if (!cpu_feature_enabled(X86_FEATURE_FRED) ||
> >+	    !guest_cpuid_has(vcpu, X86_FEATURE_FRED))
> >+		return;
> >+
> >+	/* Enable loading guest FRED MSRs from VMCS */
> >+	vm_entry_controls_setbit(vmx, VM_ENTRY_LOAD_IA32_FRED);
> >+
> >+	/*
> >+	 * Enable saving guest FRED MSRs into VMCS and loading host FRED MSRs
> >+	 * from VMCS.
> >+	 */
> >+	vm_exit_controls_setbit(vmx,
> VM_EXIT_ACTIVATE_SECONDARY_CONTROLS);
> >+	secondary_vm_exit_controls_setbit(vmx,
> >+					  SECONDARY_VM_EXIT_SAVE_IA32_FRED
> |
> >+
> SECONDARY_VM_EXIT_LOAD_IA32_FRED);
> 
> all above vmcs controls need to be cleared if guest doesn't enumerate FRED, see
> 
> https://lore.kernel.org/all/ZJYzPn7ipYfO0fLZ@google.com/

Good point, the user space could set cpuid multiple times...
 
> Clearing VM_EXIT_ACTIVATE_SECONDARY_CONTROLS may be problematic when
> new bits are added to secondary vmcs controls. Why not keep
> VM_EXIT_ACTIVATE_SECONDARY_CONTROLS always on if it is supported? or you
> see any perf impact?

I think it from the other way, why keeps hw loading it on every vmentry
even if it's not used by a guest?

Different CPUs may implement it in different ways, which we can't assume.

Other features needing it should set it separately, say with a refcount.
diff mbox series

Patch

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9186f41974ab..5d4786812664 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4423,6 +4423,9 @@  static u32 vmx_vmentry_ctrl(void)
 	if (cpu_has_perf_global_ctrl_bug())
 		vmentry_ctrl &= ~VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL;
 
+	/* Whether to load guest FRED MSRs is deferred until after set CPUID */
+	vmentry_ctrl &= ~VM_ENTRY_LOAD_IA32_FRED;
+
 	return vmentry_ctrl;
 }
 
@@ -4458,7 +4461,13 @@  static u32 vmx_vmexit_ctrl(void)
 
 static u64 vmx_secondary_vmexit_ctrl(void)
 {
-	return vmcs_config.secondary_vmexit_ctrl;
+	u64 secondary_vmexit_ctrl = vmcs_config.secondary_vmexit_ctrl;
+
+	/* Whether to save/load FRED MSRs is deferred until after set CPUID */
+	secondary_vmexit_ctrl &= ~(SECONDARY_VM_EXIT_SAVE_IA32_FRED |
+				   SECONDARY_VM_EXIT_LOAD_IA32_FRED);
+
+	return secondary_vmexit_ctrl;
 }
 
 static void vmx_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
@@ -7785,10 +7794,33 @@  static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
 		vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
 }
 
+static void vmx_vcpu_config_fred_after_set_cpuid(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	if (!cpu_feature_enabled(X86_FEATURE_FRED) ||
+	    !guest_cpuid_has(vcpu, X86_FEATURE_FRED))
+		return;
+
+	/* Enable loading guest FRED MSRs from VMCS */
+	vm_entry_controls_setbit(vmx, VM_ENTRY_LOAD_IA32_FRED);
+
+	/*
+	 * Enable saving guest FRED MSRs into VMCS and loading host FRED MSRs
+	 * from VMCS.
+	 */
+	vm_exit_controls_setbit(vmx, VM_EXIT_ACTIVATE_SECONDARY_CONTROLS);
+	secondary_vm_exit_controls_setbit(vmx,
+					  SECONDARY_VM_EXIT_SAVE_IA32_FRED |
+					  SECONDARY_VM_EXIT_LOAD_IA32_FRED);
+}
+
 static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
+	vmx_vcpu_config_fred_after_set_cpuid(vcpu);
+
 	/*
 	 * XSAVES is effectively enabled if and only if XSAVE is also exposed
 	 * to the guest.  XSAVES depends on CR4.OSXSAVE, and CR4.OSXSAVE can be