KVM: selftests: Test behavior of HWCR, a.k.a. MSR_K7_HWCR

Verify the following behavior holds true for writes and reads of HWCR from
host userspace:

* Attempts to set bits 3, 6, or 8 are ignored
* Bits 18 and 24 are the only bits that can be set
* Any bit that can be set can also be cleared

Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20230929230246.1954854-4-jmattson@google.com
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: jsmattsonjr

tools/testing/selftests/kvm/Makefile

@@ -66,6 +66,7 @@ TEST_GEN_PROGS_x86_64 += x86_64/dirty_log_page_splitting_test
 TEST_GEN_PROGS_x86_64 += x86_64/get_msr_index_features
 TEST_GEN_PROGS_x86_64 += x86_64/exit_on_emulation_failure_test
 TEST_GEN_PROGS_x86_64 += x86_64/fix_hypercall_test
+TEST_GEN_PROGS_x86_64 += x86_64/hwcr_msr_test
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_clock
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_cpuid
 TEST_GEN_PROGS_x86_64 += x86_64/hyperv_evmcs

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

@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023, Google LLC.
+ */
+
+#define _GNU_SOURCE /* for program_invocation_short_name */
+#include <sys/ioctl.h>
+
+#include "test_util.h"
+#include "kvm_util.h"
+#include "vmx.h"
+
+void test_hwcr_bit(struct kvm_vcpu *vcpu, unsigned int bit)
+{
+	const uint64_t ignored = BIT_ULL(3) | BIT_ULL(6) | BIT_ULL(8);
+	const uint64_t valid = BIT_ULL(18) | BIT_ULL(24);
+	const uint64_t legal = ignored | valid;
+	uint64_t val = BIT_ULL(bit);
+	uint64_t actual;
+	int r;
+
+	r = _vcpu_set_msr(vcpu, MSR_K7_HWCR, val);
+	TEST_ASSERT(val & ~legal ? !r : r == 1,
+		    "Expected KVM_SET_MSRS(MSR_K7_HWCR) = 0x%lx to %s",
+		    val, val & ~legal ? "fail" : "succeed");
+
+	actual = vcpu_get_msr(vcpu, MSR_K7_HWCR);
+	TEST_ASSERT(actual == (val & valid),
+		    "Bit %u: unexpected HWCR 0x%lx; expected 0x%lx",
+		    bit, actual, (val & valid));
+
+	vcpu_set_msr(vcpu, MSR_K7_HWCR, 0);
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vm *vm;
+	struct kvm_vcpu *vcpu;
+	unsigned int bit;
+
+	vm = vm_create_with_one_vcpu(&vcpu, NULL);
+
+	for (bit = 0; bit < BITS_PER_LONG; bit++)
+		test_hwcr_bit(vcpu, bit);
+
+	kvm_vm_free(vm);
+}