commit b06892bb52215df28e310f69e045d3f42a0a15ef
author Sean Christopherson <seanjc@google.com> Fri Nov 21 10:08:59 2025 -0800
committer Paolo Bonzini <bonzini@gnu.org> Tue Nov 25 23:35:47 2025 +0000
tree 21ffa4daf7cb8e4ccf904aec57b74f6f6d936358
parent 3ee16f3920e478e4e52cb0fdd6eaa5794477efa3

x86: xsave: Always verify XCR0 is actually written

When testing writes to XCR0, always verify that XCR0 reads back what was
written.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20251121180901.271486-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

x86/xsave.c

diff --git a/x86/xsave.c b/x86/xsave.c
index 72e9c67..54905e0 100644
--- a/x86/xsave.c
+++ b/x86/xsave.c
@@ -43,9 +43,17 @@
 		__TEST_VMOVDQA(ymm##r1, ymm##r2, KVM_FEP);		\
 } while (0)
 
+static void test_write_xcr0(u64 val)
+{
+	write_xcr0(val);
+
+	report(read_xcr0() == val,
+	       "Wanted XCR0 == 0x%lx, got XCR0 == 0x%lx", val, read_xcr0());
+}
+
 static __attribute__((target("avx"))) void test_avx_vmovdqa(void)
 {
-	write_xcr0(XFEATURE_MASK_FP_SSE | XFEATURE_MASK_YMM);
+	test_write_xcr0(XFEATURE_MASK_FP_SSE | XFEATURE_MASK_YMM);
 
 	TEST_VMOVDQA(0, 15);
 	TEST_VMOVDQA(1, 14);
@@ -120,9 +128,8 @@
 	       "Check CPUID.1.ECX.OSXSAVE - expect 1");
 
 	printf("\tLegal tests\n");
-	write_xcr0(XFEATURE_MASK_FP);
-	write_xcr0(XFEATURE_MASK_FP_SSE);
-	(void)read_xcr0();
+	test_write_xcr0(XFEATURE_MASK_FP);
+	test_write_xcr0(XFEATURE_MASK_FP_SSE);
 
 	if (supported_xcr0 & XFEATURE_MASK_YMM)
 		test_avx_vmovdqa();