1 files changed, 36 insertions, 21 deletions

diff --git a/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c b/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c
index 624dc725e14d..28cc66454601 100644
--- a/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c
+++ b/tools/testing/selftests/kvm/x86_64/cr4_cpuid_sync_test.c
@@ -19,30 +19,42 @@
 #include "kvm_util.h"
 #include "processor.h"
 
-static inline bool cr4_cpuid_is_sync(void)
-{
-	uint64_t cr4 = get_cr4();
-
-	return (this_cpu_has(X86_FEATURE_OSXSAVE) == !!(cr4 & X86_CR4_OSXSAVE));
-}
+#define MAGIC_HYPERCALL_PORT	0x80
 
 static void guest_code(void)
 {
-	uint64_t cr4;
+	u32 regs[4] = {
+		[KVM_CPUID_EAX] = X86_FEATURE_OSXSAVE.function,
+		[KVM_CPUID_ECX] = X86_FEATURE_OSXSAVE.index,
+	};
 
-	/* turn on CR4.OSXSAVE */
-	cr4 = get_cr4();
-	cr4 |= X86_CR4_OSXSAVE;
-	set_cr4(cr4);
+	/* CR4.OSXSAVE should be enabled by default (for selftests vCPUs). */
+	GUEST_ASSERT(get_cr4() & X86_CR4_OSXSAVE);
 
 	/* verify CR4.OSXSAVE == CPUID.OSXSAVE */
-	GUEST_ASSERT(cr4_cpuid_is_sync());
-
-	/* notify hypervisor to change CR4 */
-	GUEST_SYNC(0);
-
-	/* check again */
-	GUEST_ASSERT(cr4_cpuid_is_sync());
+	GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE));
+
+	/*
+	 * Notify hypervisor to clear CR4.0SXSAVE, do CPUID and save output,
+	 * and then restore CR4.  Do this all in  assembly to ensure no AVX
+	 * instructions are executed while OSXSAVE=0.
+	 */
+	asm volatile (
+		"out %%al, $" __stringify(MAGIC_HYPERCALL_PORT) "\n\t"
+		"cpuid\n\t"
+		"mov %%rdi, %%cr4\n\t"
+		: "+a" (regs[KVM_CPUID_EAX]),
+		  "=b" (regs[KVM_CPUID_EBX]),
+		  "+c" (regs[KVM_CPUID_ECX]),
+		  "=d" (regs[KVM_CPUID_EDX])
+		: "D" (get_cr4())
+	);
+
+	/* Verify KVM cleared OSXSAVE in CPUID when it was cleared in CR4. */
+	GUEST_ASSERT(!(regs[X86_FEATURE_OSXSAVE.reg] & BIT(X86_FEATURE_OSXSAVE.bit)));
+
+	/* Verify restoring CR4 also restored OSXSAVE in CPUID. */
+	GUEST_ASSERT(this_cpu_has(X86_FEATURE_OSXSAVE));
 
 	GUEST_DONE();
 }
@@ -62,13 +74,16 @@ int main(int argc, char *argv[])
 		vcpu_run(vcpu);
 		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
 
-		switch (get_ucall(vcpu, &uc)) {
-		case UCALL_SYNC:
+		if (vcpu->run->io.port == MAGIC_HYPERCALL_PORT &&
+		    vcpu->run->io.direction == KVM_EXIT_IO_OUT) {
 			/* emulate hypervisor clearing CR4.OSXSAVE */
 			vcpu_sregs_get(vcpu, &sregs);
 			sregs.cr4 &= ~X86_CR4_OSXSAVE;
 			vcpu_sregs_set(vcpu, &sregs);
-			break;
+			continue;
+		}
+
+		switch (get_ucall(vcpu, &uc)) {
 		case UCALL_ABORT:
 			REPORT_GUEST_ASSERT(uc);
 			break;