KVM: SVM: Provide an updated VMRUN invocation for SEV-ES guests

The run sequence is different for an SEV-ES guest compared to a legacy or
even an SEV guest. The guest vCPU register state of an SEV-ES guest will
be restored on VMRUN and saved on VMEXIT. There is no need to restore the
guest registers directly and through VMLOAD before VMRUN and no need to
save the guest registers directly and through VMSAVE on VMEXIT.

Update the svm_vcpu_run() function to skip register state saving and
restoring and provide an alternative function for running an SEV-ES guest
in vmenter.S

Additionally, certain host state is restored across an SEV-ES VMRUN. As
a result certain register states are not required to be restored upon
VMEXIT (e.g. FS, GS, etc.), so only do that if the guest is not an SEV-ES
guest.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <fb1c66d32f2194e171b95fc1a8affd6d326e10c1.1607620209.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -3700,6 +3700,9 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 	guest_enter_irqoff();
 	lockdep_hardirqs_on(CALLER_ADDR0);
 
+	if (sev_es_guest(svm->vcpu.kvm)) {
+		__svm_sev_es_vcpu_run(svm->vmcb_pa);
+	} else {
 		__svm_vcpu_run(svm->vmcb_pa, (unsigned long *)&svm->vcpu.arch.regs);
 
 #ifdef CONFIG_X86_64
@@ -3710,6 +3713,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 		loadsegment(gs, svm->host.gs);
 #endif
 #endif
+	}
 
 	/*
 	 * VMEXIT disables interrupts (host state), but tracing and lockdep
@@ -3807,14 +3811,17 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 	if (unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
 		svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
 
+	if (!sev_es_guest(svm->vcpu.kvm))
 		reload_tss(vcpu);
 
 	x86_spec_ctrl_restore_host(svm->spec_ctrl, svm->virt_spec_ctrl);
 
+	if (!sev_es_guest(svm->vcpu.kvm)) {
 		vcpu->arch.cr2 = svm->vmcb->save.cr2;
 		vcpu->arch.regs[VCPU_REGS_RAX] = svm->vmcb->save.rax;
 		vcpu->arch.regs[VCPU_REGS_RSP] = svm->vmcb->save.rsp;
 		vcpu->arch.regs[VCPU_REGS_RIP] = svm->vmcb->save.rip;
+	}
 
 	if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
 		kvm_before_interrupt(&svm->vcpu);

arch/x86/kvm/svm/svm.h

@@ -591,4 +591,9 @@ void sev_es_create_vcpu(struct vcpu_svm *svm);
 void sev_es_vcpu_load(struct vcpu_svm *svm, int cpu);
 void sev_es_vcpu_put(struct vcpu_svm *svm);
 
+/* vmenter.S */
+
+void __svm_sev_es_vcpu_run(unsigned long vmcb_pa);
+void __svm_vcpu_run(unsigned long vmcb_pa, unsigned long *regs);
+
 #endif

arch/x86/kvm/svm/vmenter.S

@@ -168,3 +168,53 @@ SYM_FUNC_START(__svm_vcpu_run)
 	pop %_ASM_BP
 	ret
 SYM_FUNC_END(__svm_vcpu_run)
+
+/**
+ * __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
+ * @vmcb_pa:	unsigned long
+ */
+SYM_FUNC_START(__svm_sev_es_vcpu_run)
+	push %_ASM_BP
+#ifdef CONFIG_X86_64
+	push %r15
+	push %r14
+	push %r13
+	push %r12
+#else
+	push %edi
+	push %esi
+#endif
+	push %_ASM_BX
+
+	/* Enter guest mode */
+	mov %_ASM_ARG1, %_ASM_AX
+	sti
+
+1:	vmrun %_ASM_AX
+	jmp 3f
+2:	cmpb $0, kvm_rebooting
+	jne 3f
+	ud2
+	_ASM_EXTABLE(1b, 2b)
+
+3:	cli
+
+#ifdef CONFIG_RETPOLINE
+	/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
+	FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+#endif
+
+	pop %_ASM_BX
+
+#ifdef CONFIG_X86_64
+	pop %r12
+	pop %r13
+	pop %r14
+	pop %r15
+#else
+	pop %esi
+	pop %edi
+#endif
+	pop %_ASM_BP
+	ret
+SYM_FUNC_END(__svm_sev_es_vcpu_run)

arch/x86/kvm/x86.c

@@ -880,6 +880,9 @@ EXPORT_SYMBOL_GPL(kvm_lmsw);
 
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
 {
+	if (vcpu->arch.guest_state_protected)
+		return;
+
 	if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE)) {
 
 		if (vcpu->arch.xcr0 != host_xcr0)
@@ -900,6 +903,9 @@ EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
 
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
 {
+	if (vcpu->arch.guest_state_protected)
+		return;
+
 	if (static_cpu_has(X86_FEATURE_PKU) &&
 	    (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
 	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU))) {