[RFC PATCH v4 7/7] KVM: selftests: Test pfncache invalidation for gmem-backed memory

[Takahiro Itazuri <itazur@amazon.com>]

Extend pfncache_gmem_test to verify pfncache invalidation paths:

 - punch_hole: fallocate(PUNCH_HOLE) on the pvclock page's guest_memfd
   frees the backing page and invalidates the pfncache.  The next
   vcpu_run re-resolves the PFN with a freshly allocated page.

 - file release: kvm_vm_free() closes the guest_memfd fd, triggering a
   full-range pfncache invalidation.

 - private-to-shared conversion: KVM_SET_MEMORY_ATTRIBUTES changes the
   pvclock page from private to shared, invalidating the pfncache.  The
   PFN is re-resolved via GUP instead of kvm_gmem_get_pfn().

Signed-off-by: Takahiro Itazuri <itazur@amazon.com>
---
 .../selftests/kvm/x86/pfncache_gmem_test.c    | 39 ++++++++++++++++---
 1 file changed, 34 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/pfncache_gmem_test.c b/tools/testing/selftests/kvm/x86/pfncache_gmem_test.c
index c61b161f3e0c..a63940c36b15 100644
--- a/tools/testing/selftests/kvm/x86/pfncache_gmem_test.c
+++ b/tools/testing/selftests/kvm/x86/pfncache_gmem_test.c
@@ -36,11 +36,10 @@ static void guest_main(vm_paddr_t pvti_pa, struct pvclock_vcpu_time_info *pvti)
 {
 	int stage = 0;
 
-	wrmsr(MSR_KVM_SYSTEM_TIME_NEW, pvti_pa | KVM_MSR_ENABLED);
-
 	for (;;) {
 		uint64_t clock;
 
+		wrmsr(MSR_KVM_SYSTEM_TIME_NEW, pvti_pa | KVM_MSR_ENABLED);
 		GUEST_ASSERT(pvti->system_time != 0);
 		clock = __pvclock_read_cycles(pvti, rdtsc());
 		GUEST_SYNC_CLOCK(stage++, clock);
@@ -97,7 +96,8 @@ static uint64_t run_and_verify_kvm_clock(struct kvm_vcpu *vcpu,
 #define PVCLOCK_GPA		(1ULL << 32)
 
 static struct kvm_vm *setup_vm(struct vm_shape shape,
-			       struct kvm_vcpu **vcpu_out)
+			       struct kvm_vcpu **vcpu_out,
+			       vm_paddr_t *pvti_gpa_out)
 {
 	struct kvm_vm *vm;
 
@@ -118,6 +118,9 @@ static struct kvm_vm *setup_vm(struct vm_shape shape,
 		vcpu_args_set(*vcpu_out, 2, (vm_paddr_t)PVCLOCK_GPA,
 			      (struct pvclock_vcpu_time_info *)PVCLOCK_GPA);
 		vm_mem_set_private(vm, PVCLOCK_GPA, getpagesize());
+
+		if (pvti_gpa_out)
+			*pvti_gpa_out = PVCLOCK_GPA;
 	} else {
 		vm_vaddr_t pvti_gva;
 		vm_paddr_t pvti_gpa;
@@ -125,6 +128,9 @@ static struct kvm_vm *setup_vm(struct vm_shape shape,
 		pvti_gva = vm_vaddr_alloc(vm, getpagesize(), 0x10000);
 		pvti_gpa = addr_gva2gpa(vm, pvti_gva);
 		vcpu_args_set(*vcpu_out, 2, pvti_gpa, pvti_gva);
+
+		if (pvti_gpa_out)
+			*pvti_gpa_out = pvti_gpa;
 	}
 
 	return vm;
@@ -139,16 +145,27 @@ static void test_no_direct_map(void)
 	};
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
+	vm_paddr_t pvti_gpa;
 	uint64_t clock = 0;
 
 	pr_info("Testing pfncache with NO_DIRECT_MAP guest_memfd\n");
 
-	vm = setup_vm(shape, &vcpu);
+	vm = setup_vm(shape, &vcpu, &pvti_gpa);
 
 	/* Verify kvm-clock works with gmem-backed pfncache (vmap KHVA) */
 	clock = run_and_verify_kvm_clock(vcpu, clock);
 	clock = run_and_verify_kvm_clock(vcpu, clock);
 
+	/*
+	 * Punch a hole in the pvclock page's guest_memfd backing.  This
+	 * invalidates the pfncache; the next vcpu_run re-resolves the PFN
+	 * with a freshly allocated page.
+	 */
+	pr_info("  punch_hole on pvclock page\n");
+	vm_guest_mem_punch_hole(vm, pvti_gpa, getpagesize());
+	clock = run_and_verify_kvm_clock(vcpu, clock);
+
+	/* Smoke test: VM teardown (closing guest_memfd) doesn't crash. */
 	kvm_vm_free(vm);
 }
 
@@ -160,16 +177,28 @@ static void test_sw_protected_vm(void)
 	};
 	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
+	vm_paddr_t pvti_gpa;
 	uint64_t clock = 0;
 
 	pr_info("Testing pfncache with SW_PROTECTED_VM (guest_memfd-backed private memory)\n");
 
-	vm = setup_vm(shape, &vcpu);
+	vm = setup_vm(shape, &vcpu, &pvti_gpa);
 
 	/* Verify kvm-clock works with gmem-backed private memory */
 	clock = run_and_verify_kvm_clock(vcpu, clock);
 	clock = run_and_verify_kvm_clock(vcpu, clock);
 
+	/* Convert pvclock page from private to shared */
+	pr_info("  converting pvclock page: private -> shared\n");
+	vm_mem_set_shared(vm, pvti_gpa, getpagesize());
+	clock = run_and_verify_kvm_clock(vcpu, 0);
+
+	/* Convert back to private */
+	pr_info("  converting pvclock page: shared -> private\n");
+	vm_mem_set_private(vm, pvti_gpa, getpagesize());
+	clock = run_and_verify_kvm_clock(vcpu, 0);
+
+	/* Smoke test: VM teardown (closing guest_memfd) doesn't crash. */
 	kvm_vm_free(vm);
 }
 
-- 
2.50.1