KVM: selftests: Play nice with AMD's AVIC errata

When AVIC, and thus IPI virtualization on AMD, is enabled, the CPU will
virtualize ICR writes.  Unfortunately, the CPU doesn't do a very good job,
as it fails to clear the BUSY bit and also allows writing ICR2[23:0],
despite them being "RESERVED MBZ".  Account for the quirky behavior in
the xapic_state test to avoid failures in a configuration that likely has
no hope of ever being enabled in production.

Link: https://lore.kernel.org/r/20240719235107.3023592-11-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/x86_64/xapic_state_test.c

@@ -13,6 +13,7 @@
 struct xapic_vcpu {
 	struct kvm_vcpu *vcpu;
 	bool is_x2apic;
+	bool has_xavic_errata;
 };
 
 static void xapic_guest_code(void)
@@ -79,12 +80,17 @@ static void ____test_icr(struct xapic_vcpu *x, uint64_t val)
 	vcpu_ioctl(vcpu, KVM_GET_LAPIC, &xapic);
 	icr = (u64)(*((u32 *)&xapic.regs[APIC_ICR])) |
 	      (u64)(*((u32 *)&xapic.regs[APIC_ICR2])) << 32;
-	if (!x->is_x2apic)
-		val &= (-1u | (0xffull << (32 + 24)));
-	else if (val & X2APIC_RSVD_BITS_MASK)
+	if (!x->is_x2apic) {
+		if (!x->has_xavic_errata)
+			val &= (-1u | (0xffull << (32 + 24)));
+	} else if (val & X2APIC_RSVD_BITS_MASK) {
 		return;
+	}
 
-	TEST_ASSERT_EQ(icr, val & ~APIC_ICR_BUSY);
+	if (x->has_xavic_errata)
+		TEST_ASSERT_EQ(icr & ~APIC_ICR_BUSY, val & ~APIC_ICR_BUSY);
+	else
+		TEST_ASSERT_EQ(icr, val & ~APIC_ICR_BUSY);
 }
 
 static void __test_icr(struct xapic_vcpu *x, uint64_t val)
@@ -236,6 +242,15 @@ int main(int argc, char *argv[])
 	vm = vm_create_with_one_vcpu(&x.vcpu, xapic_guest_code);
 	x.is_x2apic = false;
 
+	/*
+	 * AMD's AVIC implementation is buggy (fails to clear the ICR BUSY bit),
+	 * and also diverges from KVM with respect to ICR2[23:0] (KVM and Intel
+	 * drops writes, AMD does not).  Account for the errata when checking
+	 * that KVM reads back what was written.
+	 */
+	x.has_xavic_errata = host_cpu_is_amd &&
+			     get_kvm_amd_param_bool("avic");
+
 	vcpu_clear_cpuid_feature(x.vcpu, X86_FEATURE_X2APIC);
 
 	virt_pg_map(vm, APIC_DEFAULT_GPA, APIC_DEFAULT_GPA);