KVM: SVM: Use do_machine_check to pass MCE to the host

Use do_machine_check instead of INT $12 to pass MCE to the host,
the same approach VMX uses.

On a related note, there is no reason to limit the use of do_machine_check
to 64 bit targets, as is currently done for VMX. MCE handling works
for both target families.

The patch is only compile tested, for both, 64 and 32 bit targets,
someone should test the passing of the exception by injecting
some MCEs into the guest.

For future non-RFC patch, kvm_machine_check should be moved to some
appropriate header file.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Message-Id: <20200411153627.3474710-1-ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -33,6 +33,7 @@
 #include <asm/debugreg.h>
 #include <asm/kvm_para.h>
 #include <asm/irq_remapping.h>
+#include <asm/mce.h>
 #include <asm/spec-ctrl.h>
 #include <asm/cpu_device_id.h>
 
@@ -1839,6 +1840,25 @@ static bool is_erratum_383(void)
 	return true;
 }
 
+/*
+ * Trigger machine check on the host. We assume all the MSRs are already set up
+ * by the CPU and that we still run on the same CPU as the MCE occurred on.
+ * We pass a fake environment to the machine check handler because we want
+ * the guest to be always treated like user space, no matter what context
+ * it used internally.
+ */
+static void kvm_machine_check(void)
+{
+#if defined(CONFIG_X86_MCE)
+	struct pt_regs regs = {
+		.cs = 3, /* Fake ring 3 no matter what the guest ran on */
+		.flags = X86_EFLAGS_IF,
+	};
+
+	do_machine_check(&regs, 0);
+#endif
+}
+
 static void svm_handle_mce(struct vcpu_svm *svm)
 {
 	if (is_erratum_383()) {
@@ -1857,11 +1877,7 @@ static void svm_handle_mce(struct vcpu_svm *svm)
 	 * On an #MC intercept the MCE handler is not called automatically in
 	 * the host. So do it by hand here.
 	 */
-	asm volatile (
-		"int $0x12\n");
-	/* not sure if we ever come back to this point */
-
-	return;
+	kvm_machine_check();
 }
 
 static int mc_interception(struct vcpu_svm *svm)