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

Xin Li
2023-11-08T19:00:28Z

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(-)

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
--
2.42.0