[RFC PATCH 52/55] KVM: selftests: Add Hyper-V reference TSC page memory attribute test

[David Woodhouse]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

The reference TSC page is written by the host, not by the guest, so
the guest-side memory attribute tests never cover it.  Add a test
that a page at an unprotected gfn is maintained as usual, that
pointing HV_X64_MSR_REFERENCE_TSC at a gfn carrying
KVM_MEMORY_ATTRIBUTE_NW leaves the page contents untouched — on the
MSR write itself and on a subsequent KVM_SET_CLOCK-forced update —
and that re-pointing the MSR at a writable page recovers.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Assisted-by: LLM
---
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../selftests/kvm/x86/hyperv_tsc_page_attrs.c | 129 ++++++++++++++++++
 2 files changed, 130 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/x86/hyperv_tsc_page_attrs.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 47c7a4c732eb..6edeb6693375 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -89,6 +89,7 @@ TEST_GEN_PROGS_x86 += x86/hyperv_forward_hcall
 TEST_GEN_PROGS_x86 += x86/hyperv_ipi
 TEST_GEN_PROGS_x86 += x86/hyperv_svm_test
 TEST_GEN_PROGS_x86 += x86/hyperv_tlb_flush
+TEST_GEN_PROGS_x86 += x86/hyperv_tsc_page_attrs
 TEST_GEN_PROGS_x86 += x86/kvm_clock_test
 TEST_GEN_PROGS_x86 += x86/kvm_pv_test
 TEST_GEN_PROGS_x86 += x86/kvm_buslock_test
diff --git a/tools/testing/selftests/kvm/x86/hyperv_tsc_page_attrs.c b/tools/testing/selftests/kvm/x86/hyperv_tsc_page_attrs.c
new file mode 100644
index 000000000000..efa47ae69780
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/hyperv_tsc_page_attrs.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Test that KVM honours plane memory attributes when it maintains the
+ * Hyper-V reference TSC page.  A page whose gfn carries
+ * KVM_MEMORY_ATTRIBUTE_NW in the owning plane's attributes must never
+ * be written by the host, on the HV_X64_MSR_REFERENCE_TSC write or on
+ * any later masterclock update; an unprotected page keeps working, and
+ * re-pointing the MSR at a writable page recovers.
+ */
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+#include "hyperv.h"
+
+struct ms_hyperv_tsc_page {
+	volatile u32 tsc_sequence;
+	u32 reserved1;
+	volatile u64 tsc_scale;
+	volatile s64 tsc_offset;
+} __packed;
+
+#define SENTINEL_SEQ	0xdeadbeef
+#define SENTINEL_U64	0xcafef00dcafef00dULL
+
+static void guest_main(struct ms_hyperv_tsc_page *page_a, gpa_t page_a_gpa,
+		       struct ms_hyperv_tsc_page *page_b, gpa_t page_b_gpa)
+{
+	/* Set Guest OS id to enable Hyper-V emulation */
+	wrmsr(HV_X64_MSR_GUEST_OS_ID, HYPERV_LINUX_OS_ID);
+
+	/* An unprotected page is maintained by KVM as usual. */
+	wrmsr(HV_X64_MSR_REFERENCE_TSC, page_a_gpa | 0x1);
+	GUEST_ASSERT(page_a->tsc_sequence != 0);
+
+	/* Fill the page about to be protected, while it is still writable. */
+	page_b->tsc_sequence = SENTINEL_SEQ;
+	page_b->tsc_scale = SENTINEL_U64;
+	page_b->tsc_offset = SENTINEL_U64;
+
+	GUEST_SYNC(1);	/* host sets KVM_MEMORY_ATTRIBUTE_NW on page_b */
+
+	/*
+	 * Pointing the reference TSC MSR at the protected page must not
+	 * have KVM write to it: not on the MSR write itself, and not on
+	 * the masterclock update the write requests.
+	 */
+	wrmsr(HV_X64_MSR_REFERENCE_TSC, page_b_gpa | 0x1);
+	GUEST_ASSERT(page_b->tsc_sequence == SENTINEL_SEQ);
+	GUEST_ASSERT(page_b->tsc_scale == SENTINEL_U64);
+	GUEST_ASSERT(page_b->tsc_offset == SENTINEL_U64);
+
+	GUEST_SYNC(2);	/* host resets kvmclock, forcing a TSC page update */
+
+	GUEST_ASSERT(page_b->tsc_sequence == SENTINEL_SEQ);
+	GUEST_ASSERT(page_b->tsc_scale == SENTINEL_U64);
+	GUEST_ASSERT(page_b->tsc_offset == SENTINEL_U64);
+
+	/* Re-pointing the MSR at a writable page recovers. */
+	wrmsr(HV_X64_MSR_REFERENCE_TSC, page_a_gpa | 0x1);
+	GUEST_ASSERT(page_a->tsc_sequence != 0);
+
+	GUEST_DONE();
+}
+
+int main(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	struct ucall uc;
+	gva_t page_a_gva, page_b_gva;
+	gpa_t page_b_gpa;
+	int stage;
+
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_HYPERV_TIME));
+	TEST_REQUIRE(kvm_check_cap(KVM_CAP_MEMORY_ATTRIBUTES) &
+		     KVM_MEMORY_ATTRIBUTE_NW);
+	TEST_REQUIRE(sys_clocksource_is_based_on_tsc());
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_main);
+
+	vcpu_set_hv_cpuid(vcpu);
+
+	page_a_gva = vm_alloc_page(vm);
+	page_b_gva = vm_alloc_page(vm);
+	memset(addr_gva2hva(vm, page_a_gva), 0x0, getpagesize());
+	memset(addr_gva2hva(vm, page_b_gva), 0x0, getpagesize());
+	page_b_gpa = addr_gva2gpa(vm, page_b_gva);
+
+	vcpu_args_set(vcpu, 4, page_a_gva, addr_gva2gpa(vm, page_a_gva),
+		      page_b_gva, page_b_gpa);
+
+	for (stage = 1;; stage++) {
+		vcpu_run(vcpu);
+		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_ABORT:
+			REPORT_GUEST_ASSERT(uc);
+			/* NOT REACHED */
+		case UCALL_SYNC:
+			break;
+		case UCALL_DONE:
+			/* Keep in sync with guest_main() */
+			TEST_ASSERT(stage == 3, "Testing ended prematurely, stage %d",
+				    stage);
+			goto out;
+		default:
+			TEST_FAIL("Unknown ucall %lu", uc.cmd);
+		}
+
+		TEST_ASSERT(uc.args[1] == stage,
+			    "Stage %d: Unexpected sync, got %lx",
+			    stage, (ulong)uc.args[1]);
+
+		if (stage == 1)
+			vm_set_memory_attributes(vm, page_b_gpa, getpagesize(),
+						 KVM_MEMORY_ATTRIBUTE_NW);
+
+		/* Reset kvmclock triggering TSC page update */
+		if (stage == 2) {
+			struct kvm_clock_data clock = {0};
+
+			vm_ioctl(vm, KVM_SET_CLOCK, &clock);
+		}
+	}
+
+out:
+	kvm_vm_free(vm);
+}
-- 
2.50.1