1 files changed, 64 insertions, 1 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 84e5adbd0925..43dcd8c7badc 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -2,6 +2,7 @@
 
 #include <linux/console.h>
 #include <linux/cpu.h>
+#include <linux/instrumentation.h>
 #include <linux/kexec.h>
 #include <linux/memblock.h>
 #include <linux/slab.h>
@@ -21,7 +22,8 @@
 
 #include "xen-ops.h"
 
-EXPORT_SYMBOL_GPL(hypercall_page);
+DEFINE_STATIC_CALL(xen_hypercall, xen_hypercall_hvm);
+EXPORT_STATIC_CALL_TRAMP(xen_hypercall);
 
 /*
  * Pointer to the xen_vcpu_info structure or
@@ -68,6 +70,67 @@ EXPORT_SYMBOL(xen_start_flags);
  */
 struct shared_info *HYPERVISOR_shared_info = &xen_dummy_shared_info;
 
+static __ref void xen_get_vendor(void)
+{
+	init_cpu_devs();
+	cpu_detect(&boot_cpu_data);
+	get_cpu_vendor(&boot_cpu_data);
+}
+
+void xen_hypercall_setfunc(void)
+{
+	if (static_call_query(xen_hypercall) != xen_hypercall_hvm)
+		return;
+
+	if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+	     boot_cpu_data.x86_vendor == X86_VENDOR_HYGON))
+		static_call_update(xen_hypercall, xen_hypercall_amd);
+	else
+		static_call_update(xen_hypercall, xen_hypercall_intel);
+}
+
+/*
+ * Evaluate processor vendor in order to select the correct hypercall
+ * function for HVM/PVH guests.
+ * Might be called very early in boot before vendor has been set by
+ * early_cpu_init().
+ */
+noinstr void *__xen_hypercall_setfunc(void)
+{
+	void (*func)(void);
+
+	/*
+	 * Xen is supported only on CPUs with CPUID, so testing for
+	 * X86_FEATURE_CPUID is a test for early_cpu_init() having been
+	 * run.
+	 *
+	 * Note that __xen_hypercall_setfunc() is noinstr only due to a nasty
+	 * dependency chain: it is being called via the xen_hypercall static
+	 * call when running as a PVH or HVM guest. Hypercalls need to be
+	 * noinstr due to PV guests using hypercalls in noinstr code. So we
+	 * can safely tag the function body as "instrumentation ok", since
+	 * the PV guest requirement is not of interest here (xen_get_vendor()
+	 * calls noinstr functions, and static_call_update_early() might do
+	 * so, too).
+	 */
+	instrumentation_begin();
+
+	if (!boot_cpu_has(X86_FEATURE_CPUID))
+		xen_get_vendor();
+
+	if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+	     boot_cpu_data.x86_vendor == X86_VENDOR_HYGON))
+		func = xen_hypercall_amd;
+	else
+		func = xen_hypercall_intel;
+
+	static_call_update_early(xen_hypercall, func);
+
+	instrumentation_end();
+
+	return func;
+}
+
 static int xen_cpu_up_online(unsigned int cpu)
 {
 	xen_init_lock_cpu(cpu);