[PATCH v2 7/7] KVM: VMX: replace vmx_spec_ctrl_restore_host with RESTORE_HOST_SPEC_CTRL_BODY

[Paolo Bonzini]

Reuse the same assembly as SVM, just with alternatives instead
of cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS).

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/vmenter.h     |  9 +++++++--
 arch/x86/kvm/vmx/vmenter.S | 20 +++++++++++++-------
 arch/x86/kvm/vmx/vmx.c     | 25 -------------------------
 arch/x86/kvm/vmx/vmx.h     |  1 -
 4 files changed, 20 insertions(+), 35 deletions(-)

diff --git a/arch/x86/kvm/vmenter.h b/arch/x86/kvm/vmenter.h
index 84951e186859..93db912eef44 100644
--- a/arch/x86/kvm/vmenter.h
+++ b/arch/x86/kvm/vmenter.h
@@ -55,7 +55,12 @@
 #ifdef CONFIG_X86_64
 	mov PER_CPU_VAR(x86_spec_ctrl_current), %rdx
 	cmp \guest_spec_ctrl, %rdx
-	je \label
+	/*
+	 * For legacy IBRS, the IBRS bit always needs to be written after
+	 * transitioning from a less privileged predictor mode, regardless of
+	 * whether the guest/host values differ.
+	 */
+	ALTERNATIVE __stringify(je \label), "", X86_FEATURE_KERNEL_IBRS
 	movl %edx, %eax
 	shr $32, %rdx
 #else
@@ -66,7 +71,7 @@
 	mov 4 + \guest_spec_ctrl, %edi
 	xor %edx, %edi
 	or %edi, %esi
-	je \label
+	ALTERNATIVE __stringify(je \label), "", X86_FEATURE_KERNEL_IBRS
 #endif
 	wrmsr
 .endm
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index 7dd9bac0e454..294407dfc24f 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -105,9 +105,9 @@ SYM_FUNC_START(__vmx_vcpu_run)
 	 * Unlike AMD there's no V_SPEC_CTRL here, so do not leave the body
 	 * out of line.  Clobbers RAX, RCX, RDX, RSI.
 	 */
-	ALTERNATIVE "jmp .Lspec_ctrl_done", "", X86_FEATURE_MSR_SPEC_CTRL
-	RESTORE_GUEST_SPEC_CTRL_BODY VMX_spec_ctrl(%_ASM_DI), .Lspec_ctrl_done
-.Lspec_ctrl_done:
+	ALTERNATIVE "jmp .Lspec_ctrl_guest_done", "", X86_FEATURE_MSR_SPEC_CTRL
+	RESTORE_GUEST_SPEC_CTRL_BODY VMX_spec_ctrl(%_ASM_DI), .Lspec_ctrl_guest_done
+.Lspec_ctrl_guest_done:
 
 	/*
 	 * Since vmentry is serializing on affected CPUs, there's no need for
@@ -252,16 +252,22 @@ SYM_INNER_LABEL_ALIGN(vmx_vmexit, SYM_L_GLOBAL)
 	FILL_RETURN_BUFFER %_ASM_CX, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_VMEXIT,\
 			   X86_FEATURE_RSB_VMEXIT_LITE
 
-	pop %_ASM_ARG2	/* @flags */
-	pop %_ASM_ARG1	/* @vmx */
-
-	call vmx_spec_ctrl_restore_host
+	/* Clobbers RAX, RCX, RDX, RSI.  */
+	ALTERNATIVE "jmp .Lspec_ctrl_host_done", "", X86_FEATURE_MSR_SPEC_CTRL
+	mov WORD_SIZE(%_ASM_SP), %_ASM_DI
+	RESTORE_HOST_SPEC_CTRL_BODY VMX_spec_ctrl(%_ASM_DI), (%_ASM_SP), .Lspec_ctrl_host_done
+.Lspec_ctrl_host_done:
 
 	CLEAR_BRANCH_HISTORY_VMEXIT
 
 	/* Put return value in AX */
 	mov %_ASM_BX, %_ASM_AX
 
+	/* Pop our saved arguments from the stack */
+	pop %_ASM_BX
+	pop %_ASM_BX
+
+	/* ... and then the callee-save registers */
 	pop %_ASM_BX
 #ifdef CONFIG_X86_64
 	pop %r12
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a8039b0f9392..b033f611fa04 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7388,31 +7388,6 @@ void noinstr vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
 	}
 }
 
-void noinstr vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx,
-					unsigned int flags)
-{
-	u64 hostval = this_cpu_read(x86_spec_ctrl_current);
-
-	if (!cpu_feature_enabled(X86_FEATURE_MSR_SPEC_CTRL))
-		return;
-
-	if (flags & KVM_ENTER_SAVE_SPEC_CTRL)
-		vmx->spec_ctrl = native_rdmsrq(MSR_IA32_SPEC_CTRL);
-
-	/*
-	 * If the guest/host SPEC_CTRL values differ, restore the host value.
-	 *
-	 * For legacy IBRS, the IBRS bit always needs to be written after
-	 * transitioning from a less privileged predictor mode, regardless of
-	 * whether the guest/host values differ.
-	 */
-	if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) ||
-	    vmx->spec_ctrl != hostval)
-		native_wrmsrq(MSR_IA32_SPEC_CTRL, hostval);
-
-	barrier_nospec();
-}
-
 static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu,
 					     bool force_immediate_exit)
 {
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index be6a1dc2f69f..f62007a5c2a7 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -367,7 +367,6 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
 struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr);
 void pt_update_intercept_for_msr(struct kvm_vcpu *vcpu);
 void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp);
-void vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx, unsigned int flags);
 unsigned int __vmx_vcpu_enter_flags(struct vcpu_vmx *vmx);
 bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned int flags);
 void vmx_ept_load_pdptrs(struct kvm_vcpu *vcpu);
-- 
2.52.0