Re: [RFC PATCH v2 3/3] KVM: selftests: Add set_memory_region_io to test memslots for MMIO BARs

[Yan Zhao]

On Fri, Jan 05, 2024 at 02:25:26PM +0800, Yuan Yao wrote:
> On Wed, Jan 03, 2024 at 04:45:35PM +0800, Yan Zhao wrote:
> > Added a selftest set_memory_region_io to test memslots for MMIO BARs.
> 
> Emm.. "set_memory_region_io" doesn't represent the real testing purpose,
> but not sure if things like "memory_region_page_refcount_test" become
> better...
Hmm, memory_region_io_page_test?
Not just ref count is tested.
Without patch 1, mapping of pages will even fail.

> 
> > The MMIO BARs' backends are compound/non-compound huge pages serving as
> > device resources allocated by a mock device driver.
> >
> > This selftest will assert and report "errno=14 - Bad address" in vcpu_run()
> > if any failure is met to add such MMIO BAR memslots.
> > After MMIO memslots removal, page reference counts of the device resources
> > are also checked.
> >
> > As this selftest will interacts with a mock device "/dev/kvm_mock_device",
> > it depends on test driver test_kvm_mock_device.ko in the kernel.
> > CONFIG_TEST_KVM_MOCK_DEVICE=m must be enabled in the kernel.
> >
> > Currently, this selftest is only compiled for __x86_64__.
> >
> > Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
...
> > +static void *vcpu_worker(void *data)
> > +{
> > +	struct kvm_vcpu *vcpu = data;
> > +	struct kvm_run *run = vcpu->run;
> > +	struct ucall uc;
> > +	uint64_t cmd;
> > +
> > +	/*
> > +	 * Loop until the guest is done.  Re-enter the guest on all MMIO exits,
> > +	 * which will occur if the guest attempts to access a memslot after it
> > +	 * has been deleted or while it is being moved .
> > +	 */
> > +	while (1) {
> > +		vcpu_run(vcpu);
> > +
> > +		if (run->exit_reason == KVM_EXIT_IO) {
> > +			cmd = get_ucall(vcpu, &uc);
> > +			if (cmd != UCALL_SYNC)
> > +				break;
> > +
> > +			sem_post(&vcpu_ready);
> > +			continue;
> > +		}
> > +
> > +		if (run->exit_reason != KVM_EXIT_MMIO)
> > +			break;
> 
> Can the KVM_EXIT_MMIO happen on x86 ? IIUC the accessed GVAs
> in guest code have 1:1 mapping to MEM_REGION_GPA_BASE, which
> is covered by the memslot, and the memory slot is there
> until the guest code path done.
> 
It can, if the GPAs accessed by guest code are not even mapped as a
memslot.
This check is to ensure GPAs are read from the testing memslot for mock IO.

> > +
> > +		TEST_ASSERT(!run->mmio.is_write, "Unexpected exit mmio write");
> > +		TEST_ASSERT(run->mmio.len == 8,
> > +			    "Unexpected exit mmio size = %u", run->mmio.len);
> > +
> > +		TEST_ASSERT(run->mmio.phys_addr < MEM_REGION_GPA_BASE ||
> > +			    run->mmio.phys_addr >= MEM_REGION_GPA_BASE + bar_size,
> > +			    "Unexpected exit mmio address = 0x%llx",
> > +			    run->mmio.phys_addr);
> 
> Ditto, I just think you don't need this part in this testing.
> 
> > +	}
> > +
> > +	if (run->exit_reason == KVM_EXIT_IO && cmd == UCALL_ABORT)
> > +		REPORT_GUEST_ASSERT(uc);
> > +
> > +	return NULL;
> > +}
> > +
> > +static void wait_for_vcpu(void)
> > +{
> > +	struct timespec ts;
> > +
> > +	TEST_ASSERT(!clock_gettime(CLOCK_REALTIME, &ts),
> > +		    "clock_gettime() failed: %d\n", errno);
> > +
> > +	ts.tv_sec += 2;
> > +	TEST_ASSERT(!sem_timedwait(&vcpu_ready, &ts),
> > +		    "sem_timedwait() failed: %d\n", errno);
> > +
> > +	/* Wait for the vCPU thread to reenter the guest. */
> > +	usleep(100000);
> 
> In this testing it's not needed.
> Because you only check guest state after guest code path done,
> so pthread_join() is enough there.
Right. Just keep to the convention :)

> 
> > +}
> > +
> > +static void test_kvm_mock_device_bar(bool compound)
> > +{
> > +	struct kvm_vm *vm;
> > +	void *mem;
> > +	struct kvm_vcpu *vcpu;
> > +	pthread_t vcpu_thread;
> > +	int fd, ret;
> > +	u32 param_compound = compound;
> > +	u32 inequal = 0;
> > +
> > +	fd = open("/dev/kvm_mock_device", O_RDWR);
> > +	if (fd < 0) {
> > +		pr_info("Please ensure \"CONFIG_TEST_KVM_MOCK_DEVICE=m\" is enabled in the kernel");
> > +		pr_info(", and execute\n\"modprobe test_kvm_mock_device\n");
> > +	}
> > +	TEST_ASSERT(fd >= 0, "Failed to open kvm mock device.");
> 
> Minor:
> May better to move this part into main(), highlight it's a
> must have dependency at beginning.
I don't think so.
main() can do other tests that are not relying on the mock device.
Actually I'm not even sure if this test needs to be put in
set_memory_region_test.c.

> 
> > +
> > +	ret = ioctl(fd, KVM_MOCK_DEVICE_GET_BAR_SIZE, &bar_size);
> > +	TEST_ASSERT(ret == 0, "Failed to get bar size of kvm mock device");
> > +
> > +	ret = ioctl(fd, KVM_MOCK_DEVICE_PREPARE_RESOURCE, &param_compound);
> > +	TEST_ASSERT(ret == 0, "Failed to prepare resource of kvm mock device");
> > +
> > +	mem = mmap(NULL, (size_t)bar_size, PROT_READ | PROT_WRITE, MAP_SHARED,
> > +		   fd, 0);
> > +	TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() kvm mock device bar");
> > +
> > +	*(u64 *)mem = BASE_VAL;
> > +	*(u64 *)(mem + RANDOM_OFFSET) = RANDOM_VAL;
> > +
> > +	vm = vm_create_with_one_vcpu(&vcpu, guest_code_read_bar);
> > +
> > +	vm_set_user_memory_region(vm, MEM_REGION_SLOT_ID, 0, MEM_REGION_GPA_BASE,
> > +				  bar_size, mem);
> > +
> > +	virt_map(vm, MEM_REGION_GPA_BASE, MEM_REGION_GPA_BASE,
> > +		 (RANDOM_OFFSET / getpagesize()) + 1);
> > +
> > +	pthread_create(&vcpu_thread, NULL, vcpu_worker, vcpu);
> > +
> > +	/* Ensure the guest thread is spun up. */
> > +	wait_for_vcpu();
> > +
> > +	pthread_join(vcpu_thread, NULL);
> > +
> > +	vm_set_user_memory_region(vm, MEM_REGION_SLOT_ID, 0, 0, 0, 0);
> > +	kvm_vm_free(vm);
> > +
> > +	ret = ioctl(fd, KVM_MOCK_DEVICE_CHECK_BACKEND_REF, &inequal);
> > +	TEST_ASSERT(ret == 0 && inequal == 0, "Incorrect resource ref of KVM device");
> > +
> > +	munmap(mem, bar_size);
> > +	close(fd);
> > +}
> > +
> > +static void test_non_compound_backend(void)
> > +{
> > +	pr_info("Testing non-compound huge page backend for mem slot\n");
> > +	test_kvm_mock_device_bar(false);
> > +}
> > +
> > +static void test_compound_backend(void)
> > +{
> > +	pr_info("Testing compound huge page backend for mem slot\n");
> > +	test_kvm_mock_device_bar(true);
> > +}
> > +
> > +int main(int argc, char *argv[])
> > +{
> > +#ifdef __x86_64__
> > +	test_compound_backend();
> > +	if (non_compound_supported)
> 
> Nobody set this, but the mock device looks already supported
> it, so how about just run the 2 testings directly here ?
Without the series "allow mapping non-refcounted pages" [1], the test
test_non_compound_backend() will simply fail.

I added this test case is to show it non-compound pages as backend can
also be tested with this selftest. And actually, I did tested that
series with this selftets.

So, can remove the "if non_compound_supported" after [1] is merged.

[1] https://lore.kernel.org/all/20230911021637.1941096-1-stevensd@xxxxxxxxxx/,

Thanks

> 
> > +		test_non_compound_backend();
> > +#endif
> > +
> > +	return 0;
> > +}
> > --
> > 2.17.1
> >
>