linux-kernel - [PATCH v17 24/24] KVM: selftests: Add guest_memfd testcase to fault-in on !mmap()'d memory

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Message-ID: <20250729225455.670324-25-seanjc@google.com>
Date: Tue, 29 Jul 2025 15:54:55 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Ira Weiny <ira.weiny@...el.com>, Gavin Shan <gshan@...hat.com>, Shivank Garg <shivankg@....com>, 
	Vlastimil Babka <vbabka@...e.cz>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	David Hildenbrand <david@...hat.com>, Fuad Tabba <tabba@...gle.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Tao Chan <chentao@...inos.cn>, 
	James Houghton <jthoughton@...gle.com>
Subject: [PATCH v17 24/24] KVM: selftests: Add guest_memfd testcase to
 fault-in on !mmap()'d memory

Add a guest_memfd testcase to verify that a vCPU can fault-in guest_memfd
memory that supports mmap(), but that is not currently mapped into host
userspace and/or has a userspace address (in the memslot) that points at
something other than the target guest_memfd range.  Mapping guest_memfd
memory into the guest is supposed to operate completely independently from
any userspace mappings.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 .../testing/selftests/kvm/guest_memfd_test.c  | 64 +++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
index 088053d5f0f5..b86bf89a71e0 100644
--- a/tools/testing/selftests/kvm/guest_memfd_test.c
+++ b/tools/testing/selftests/kvm/guest_memfd_test.c
@@ -13,6 +13,7 @@
 
 #include <linux/bitmap.h>
 #include <linux/falloc.h>
+#include <linux/sizes.h>
 #include <setjmp.h>
 #include <signal.h>
 #include <sys/mman.h>
@@ -21,6 +22,7 @@
 
 #include "kvm_util.h"
 #include "test_util.h"
+#include "ucall_common.h"
 
 static void test_file_read_write(int fd)
 {
@@ -298,6 +300,66 @@ static void test_guest_memfd(unsigned long vm_type)
 	kvm_vm_free(vm);
 }
 
+static void guest_code(uint8_t *mem, uint64_t size)
+{
+	size_t i;
+
+	for (i = 0; i < size; i++)
+		__GUEST_ASSERT(mem[i] == 0xaa,
+			       "Guest expected 0xaa at offset %lu, got 0x%x", i, mem[i]);
+
+	memset(mem, 0xff, size);
+	GUEST_DONE();
+}
+
+static void test_guest_memfd_guest(void)
+{
+	/*
+	 * Skip the first 4gb and slot0.  slot0 maps <1gb and is used to back
+	 * the guest's code, stack, and page tables, and low memory contains
+	 * the PCI hole and other MMIO regions that need to be avoided.
+	 */
+	const uint64_t gpa = SZ_4G;
+	const int slot = 1;
+
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	uint8_t *mem;
+	size_t size;
+	int fd, i;
+
+	if (!kvm_has_cap(KVM_CAP_GUEST_MEMFD_MMAP))
+		return;
+
+	vm = __vm_create_shape_with_one_vcpu(VM_SHAPE_DEFAULT, &vcpu, 1, guest_code);
+
+	TEST_ASSERT(vm_check_cap(vm, KVM_CAP_GUEST_MEMFD_MMAP),
+		    "Default VM type should always support guest_memfd mmap()");
+
+	size = vm->page_size;
+	fd = vm_create_guest_memfd(vm, size, GUEST_MEMFD_FLAG_MMAP);
+	vm_set_user_memory_region2(vm, slot, KVM_MEM_GUEST_MEMFD, gpa, size, NULL, fd, 0);
+
+	mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() on guest_memfd failed");
+	memset(mem, 0xaa, size);
+	munmap(mem, size);
+
+	virt_pg_map(vm, gpa, gpa);
+	vcpu_args_set(vcpu, 2, gpa, size);
+	vcpu_run(vcpu);
+
+	TEST_ASSERT_EQ(get_ucall(vcpu, NULL), UCALL_DONE);
+
+	mem = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	TEST_ASSERT(mem != MAP_FAILED, "mmap() on guest_memfd failed");
+	for (i = 0; i < size; i++)
+		TEST_ASSERT_EQ(mem[i], 0xff);
+
+	close(fd);
+	kvm_vm_free(vm);
+}
+
 int main(int argc, char *argv[])
 {
 	unsigned long vm_types, vm_type;
@@ -314,4 +376,6 @@ int main(int argc, char *argv[])
 
 	for_each_set_bit(vm_type, &vm_types, BITS_PER_TYPE(vm_types))
 		test_guest_memfd(vm_type);
+
+	test_guest_memfd_guest();
 }
-- 
2.50.1.552.g942d659e1b-goog