Re: [PATCH 04/10] KVM: x86: do not go through ctxt->ops when emulating rsm

[Sean Christopherson]

On Fri, Oct 28, 2022, kernel test robot wrote:
> All warnings (new ones prefixed by >>):
> 
>    arch/x86/kvm/smm.c: In function 'emulator_leave_smm':
> >> arch/x86/kvm/smm.c:503:33: warning: unused variable 'efer' [-Wunused-variable]
>      503 |         unsigned long cr0, cr4, efer;
>          |                                 ^~~~
> >> arch/x86/kvm/smm.c:503:28: warning: unused variable 'cr4' [-Wunused-variable]
>      503 |         unsigned long cr0, cr4, efer;
>          |                            ^~~
> 
> 
> vim +/efer +503 arch/x86/kvm/smm.c
> 
> e2881deb76e87c Paolo Bonzini 2022-10-27  499  
> e2881deb76e87c Paolo Bonzini 2022-10-27  500  int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
> e2881deb76e87c Paolo Bonzini 2022-10-27  501  {
> e2881deb76e87c Paolo Bonzini 2022-10-27  502  	struct kvm_vcpu *vcpu = ctxt->vcpu;
> e2881deb76e87c Paolo Bonzini 2022-10-27 @503  	unsigned long cr0, cr4, efer;
> e2881deb76e87c Paolo Bonzini 2022-10-27  504  	char buf[512];
> e2881deb76e87c Paolo Bonzini 2022-10-27  505  	u64 smbase;
> e2881deb76e87c Paolo Bonzini 2022-10-27  506  	int ret;
> e2881deb76e87c Paolo Bonzini 2022-10-27  507  
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  508  	smbase = vcpu->arch.smbase;
> e2881deb76e87c Paolo Bonzini 2022-10-27  509  
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  510  	ret = kvm_vcpu_read_guest(vcpu, smbase + 0xfe00, buf, sizeof(buf));
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  511  	if (ret < 0)
> e2881deb76e87c Paolo Bonzini 2022-10-27  512  		return X86EMUL_UNHANDLEABLE;
> e2881deb76e87c Paolo Bonzini 2022-10-27  513  
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  514  	if ((vcpu->arch.hflags & HF_SMM_INSIDE_NMI_MASK) == 0)
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  515  		static_call(kvm_x86_set_nmi_mask)(vcpu, false);
> e2881deb76e87c Paolo Bonzini 2022-10-27  516  
> e2881deb76e87c Paolo Bonzini 2022-10-27  517  	kvm_smm_changed(vcpu, false);
> e2881deb76e87c Paolo Bonzini 2022-10-27  518  
> e2881deb76e87c Paolo Bonzini 2022-10-27  519  	/*
> e2881deb76e87c Paolo Bonzini 2022-10-27  520  	 * Get back to real mode, to prepare a safe state in which to load
> e2881deb76e87c Paolo Bonzini 2022-10-27  521  	 * CR0/CR3/CR4/EFER.  It's all a bit more complicated if the vCPU
> e2881deb76e87c Paolo Bonzini 2022-10-27  522  	 * supports long mode.
> e2881deb76e87c Paolo Bonzini 2022-10-27  523  	 */
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  524  #ifdef CONFIG_X86_64
> 9842725ac4bb94 Paolo Bonzini 2022-10-27  525  	if (guest_cpuid_has(vcpu, X86_FEATURE_LM)) {

My suggestion from the previous version[*] should still work.  Copy+pasted below
for convenience, may or may not apply cleanly.

https://lore.kernel.org/all/Y0nO0quQnVFQruPM@xxxxxxxxxx

---
 arch/x86/kvm/smm.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index 41ca128478fc..740fca1cf3a3 100644
--- a/arch/x86/kvm/smm.c
+++ b/arch/x86/kvm/smm.c
@@ -500,6 +500,8 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
 {
 	struct kvm_vcpu *vcpu = ctxt->vcpu;
+	bool is_64bit_vcpu = IS_ENABLED(CONFIG_X86_64) &&
+			     guest_cpuid_has(vcpu, X86_FEATURE_LM);
 	unsigned long cr0, cr4, efer;
 	char buf[512];
 	u64 smbase;
@@ -521,8 +523,7 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
 	 * CR0/CR3/CR4/EFER.  It's all a bit more complicated if the vCPU
 	 * supports long mode.
 	 */
-#ifdef CONFIG_X86_64
-	if (guest_cpuid_has(vcpu, X86_FEATURE_LM)) {
+	if (is_64bit_vcpu) {
 		struct kvm_segment cs_desc;
 
 		/* Zero CR4.PCIDE before CR0.PG.  */
@@ -536,15 +537,13 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
 		cs_desc.s = cs_desc.g = cs_desc.present = 1;
 		kvm_set_segment(vcpu, &cs_desc, VCPU_SREG_CS);
 	}
-#endif
 
 	/* For the 64-bit case, this will clear EFER.LMA.  */
 	cr0 = kvm_read_cr0(vcpu);
 	if (cr0 & X86_CR0_PE)
 		kvm_set_cr0(vcpu, cr0 & ~(X86_CR0_PG | X86_CR0_PE));
 
-#ifdef CONFIG_X86_64
-	if (guest_cpuid_has(vcpu, X86_FEATURE_LM)) {
+	if (is_64bit_vcpu) {
 		/* Clear CR4.PAE before clearing EFER.LME. */
 		cr4 = kvm_read_cr4(vcpu);
 		if (cr4 & X86_CR4_PAE)
@@ -554,7 +553,6 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
 		efer = 0;
 		kvm_set_msr(vcpu, MSR_EFER, efer);
 	}
-#endif
 
 	/*
 	 * Give leave_smm() a chance to make ISA-specific changes to the vCPU
@@ -565,7 +563,7 @@ int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
 		return X86EMUL_UNHANDLEABLE;
 
 #ifdef CONFIG_X86_64
-	if (guest_cpuid_has(vcpu, X86_FEATURE_LM))
+	if (is_64bit_vcpu)
 		return rsm_load_state_64(ctxt, buf);
 	else
 #endif

base-commit: 8b86d27cc60a150252b04989de818ad4ec85f899
--