[PATCH v4 29/30] KVM: selftests: Define cpu_relax() helpers for s390 and x86

[Paolo Bonzini]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

Add cpu_relax() for s390 and x86 for use in arch-agnostic tests.  arm64
already defines its own version.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20220226001546.360188-28-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/include/s390x/processor.h  | 8 ++++++++
 tools/testing/selftests/kvm/include/x86_64/processor.h | 5 +++++
 2 files changed, 13 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/s390x/processor.h b/tools/testing/selftests/kvm/include/s390x/processor.h
index e0e96a5f608c..255c9b990f4c 100644
--- a/tools/testing/selftests/kvm/include/s390x/processor.h
+++ b/tools/testing/selftests/kvm/include/s390x/processor.h
@@ -5,6 +5,8 @@
 #ifndef SELFTEST_KVM_PROCESSOR_H
 #define SELFTEST_KVM_PROCESSOR_H
 
+#include <linux/compiler.h>
+
 /* Bits in the region/segment table entry */
 #define REGION_ENTRY_ORIGIN	~0xfffUL /* region/segment table origin	   */
 #define REGION_ENTRY_PROTECT	0x200	 /* region protection bit	   */
@@ -19,4 +21,10 @@
 #define PAGE_PROTECT	0x200		/* HW read-only bit  */
 #define PAGE_NOEXEC	0x100		/* HW no-execute bit */
 
+/* Is there a portable way to do this? */
+static inline void cpu_relax(void)
+{
+	barrier();
+}
+
 #endif
diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index 8a470da7b71a..37db341d4cc5 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -363,6 +363,11 @@ static inline unsigned long get_xmm(int n)
 	return 0;
 }
 
+static inline void cpu_relax(void)
+{
+	asm volatile("rep; nop" ::: "memory");
+}
+
 bool is_intel_cpu(void);
 bool is_amd_cpu(void);
 
-- 
2.31.1