[PATCH kvm-unit-tests] memory: Skip tests for instructions that are absent

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

Checking that instructions are absent is broken when running with CPU
models other than the bare metal processor's, because neither VMX nor SVM have
intercept controls for the instructions.

This can even happen with "-cpu max" when running under nested
virtualization, which is the current situation in the Fedora KVM job
on Cirrus-CI:

FAIL: clflushopt (ABSENT)
FAIL: clwb (ABSENT)

In other words it looks like the features have been marked as disabled
in the L0 host, while the hardware supports them.

Reported-by: Thomas Huth <thuth@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 x86/memory.c | 69 +++++++++++++++++++++++++++-------------------------
 1 file changed, 36 insertions(+), 33 deletions(-)

diff --git a/x86/memory.c b/x86/memory.c
index 351e7c0..ffd4eeb 100644
--- a/x86/memory.c
+++ b/x86/memory.c
@@ -25,53 +25,56 @@ static void handle_ud(struct ex_regs *regs)
 
 int main(int ac, char **av)
 {
-	int expected;
-
 	handle_exception(UD_VECTOR, handle_ud);
 
 	/* 3-byte instructions: */
 	isize = 3;
 
-	expected = !this_cpu_has(X86_FEATURE_CLFLUSH); /* CLFLUSH */
-	ud = 0;
-	asm volatile("clflush (%0)" : : "b" (&target));
-	report(ud == expected, "clflush (%s)", expected ? "ABSENT" : "present");
+	if (this_cpu_has(X86_FEATURE_CLFLUSH)) { /* CLFLUSH */
+		ud = 0;
+		asm volatile("clflush (%0)" : : "b" (&target));
+		report(!ud, "clflush");
+	}
 
-	expected = !this_cpu_has(X86_FEATURE_XMM); /* SSE */
-	ud = 0;
-	asm volatile("sfence");
-	report(ud == expected, "sfence (%s)", expected ? "ABSENT" : "present");
+	if (this_cpu_has(X86_FEATURE_XMM)) { /* SSE */
+		ud = 0;
+		asm volatile("sfence");
+		report(!ud, "sfence");
+	}
 
-	expected = !this_cpu_has(X86_FEATURE_XMM2); /* SSE2 */
-	ud = 0;
-	asm volatile("lfence");
-	report(ud == expected, "lfence (%s)", expected ? "ABSENT" : "present");
+	if (this_cpu_has(X86_FEATURE_XMM2)) { /* SSE2 */
+		ud = 0;
+		asm volatile("lfence");
+		report(!ud, "lfence");
 
-	ud = 0;
-	asm volatile("mfence");
-	report(ud == expected, "mfence (%s)", expected ? "ABSENT" : "present");
+		ud = 0;
+		asm volatile("mfence");
+		report(!ud, "mfence");
+	}
 
 	/* 4-byte instructions: */
 	isize = 4;
 
-	expected = !this_cpu_has(X86_FEATURE_CLFLUSHOPT); /* CLFLUSHOPT */
-	ud = 0;
-	/* clflushopt (%rbx): */
-	asm volatile(".byte 0x66, 0x0f, 0xae, 0x3b" : : "b" (&target));
-	report(ud == expected, "clflushopt (%s)",
-	       expected ? "ABSENT" : "present");
+	if (this_cpu_has(X86_FEATURE_CLFLUSHOPT)) { /* CLFLUSHOPT */
+		ud = 0;
+		/* clflushopt (%rbx): */
+		asm volatile(".byte 0x66, 0x0f, 0xae, 0x3b" : : "b" (&target));
+		report(!ud, "clflushopt");
+	}
 
-	expected = !this_cpu_has(X86_FEATURE_CLWB); /* CLWB */
-	ud = 0;
-	/* clwb (%rbx): */
-	asm volatile(".byte 0x66, 0x0f, 0xae, 0x33" : : "b" (&target));
-	report(ud == expected, "clwb (%s)", expected ? "ABSENT" : "present");
+	if (this_cpu_has(X86_FEATURE_CLWB)) { /* CLWB */
+		ud = 0;
+		/* clwb (%rbx): */
+		asm volatile(".byte 0x66, 0x0f, 0xae, 0x33" : : "b" (&target));
+		report(!ud, "clwb");
+	}
 
-	expected = !this_cpu_has(X86_FEATURE_PCOMMIT); /* PCOMMIT */
-	ud = 0;
-	/* pcommit: */
-	asm volatile(".byte 0x66, 0x0f, 0xae, 0xf8");
-	report(ud == expected, "pcommit (%s)", expected ? "ABSENT" : "present");
+	if (this_cpu_has(X86_FEATURE_PCOMMIT)) { /* PCOMMIT */
+		ud = 0;
+		/* pcommit: */
+		asm volatile(".byte 0x66, 0x0f, 0xae, 0xf8");
+		report(!ud, "pcommit");
+	}
 
 	return report_summary();
 }
-- 
2.39.2