x86/virt: KVM: Move "disable SVM" helper into KVM SVM

Move cpu_svm_disable() into KVM proper now that all hardware
virtualization management is routed through KVM.  Remove the now-empty
virtext.h.

No functional change intended.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-17-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/svm/svm.c

@@ -42,8 +42,6 @@
 #include <asm/reboot.h>
 #include <asm/fpu/api.h>
 
-#include <asm/virtext.h>
-
 #include <trace/events/ipi.h>
 
 #include "trace.h"
@@ -582,9 +580,32 @@ void __svm_write_tsc_multiplier(u64 multiplier)
 	preempt_enable();
 }
 
+static inline void kvm_cpu_svm_disable(void)
+{
+	uint64_t efer;
+
+	wrmsrl(MSR_VM_HSAVE_PA, 0);
+	rdmsrl(MSR_EFER, efer);
+	if (efer & EFER_SVME) {
+		/*
+		 * Force GIF=1 prior to disabling SVM to ensure INIT and NMI
+		 * aren't blocked, e.g. if a fatal error occurred between CLGI
+		 * and STGI.  Note, STGI may #UD if SVM is disabled from NMI
+		 * context between reading EFER and executing STGI.  In that
+		 * case, GIF must already be set, otherwise the NMI would have
+		 * been blocked, so just eat the fault.
+		 */
+		asm_volatile_goto("1: stgi\n\t"
+				  _ASM_EXTABLE(1b, %l[fault])
+				  ::: "memory" : fault);
+fault:
+		wrmsrl(MSR_EFER, efer & ~EFER_SVME);
+	}
+}
+
 static void svm_emergency_disable(void)
 {
-	cpu_svm_disable();
+	kvm_cpu_svm_disable();
 }
 
 static void svm_hardware_disable(void)
@@ -593,7 +614,7 @@ static void svm_hardware_disable(void)
 	if (tsc_scaling)
 		__svm_write_tsc_multiplier(SVM_TSC_RATIO_DEFAULT);
 
-	cpu_svm_disable();
+	kvm_cpu_svm_disable();
 
 	amd_pmu_disable_virt();
 }