Re: [PATCH v2 2/2] selftests: kvm: Add mem_slot_test test

[Andrew Jones]

On Fri, Apr 03, 2020 at 02:24:28PM -0300, Wainer dos Santos Moschetta wrote:
> This patch introduces the mem_slot_test test which checks
> an VM can have added memory slots up to the limit defined in
> KVM_CAP_NR_MEMSLOTS. Then attempt to add one more slot to
> verify it fails as expected.
> 
> Signed-off-by: Wainer dos Santos Moschetta <wainersm@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/.gitignore      |  1 +
>  tools/testing/selftests/kvm/Makefile        |  3 +
>  tools/testing/selftests/kvm/mem_slot_test.c | 85 +++++++++++++++++++++
>  3 files changed, 89 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/mem_slot_test.c
> 
> diff --git a/tools/testing/selftests/kvm/.gitignore b/tools/testing/selftests/kvm/.gitignore
> index 16877c3daabf..232f24d6931a 100644
> --- a/tools/testing/selftests/kvm/.gitignore
> +++ b/tools/testing/selftests/kvm/.gitignore
> @@ -22,3 +22,4 @@
>  /dirty_log_test
>  /kvm_create_max_vcpus
>  /steal_time
> +/mem_slot_test
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 712a2ddd2a27..69b44178f48b 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -33,12 +33,14 @@ TEST_GEN_PROGS_x86_64 += demand_paging_test
>  TEST_GEN_PROGS_x86_64 += dirty_log_test
>  TEST_GEN_PROGS_x86_64 += kvm_create_max_vcpus
>  TEST_GEN_PROGS_x86_64 += steal_time
> +TEST_GEN_PROGS_x86_64 += mem_slot_test
>  
>  TEST_GEN_PROGS_aarch64 += clear_dirty_log_test
>  TEST_GEN_PROGS_aarch64 += demand_paging_test
>  TEST_GEN_PROGS_aarch64 += dirty_log_test
>  TEST_GEN_PROGS_aarch64 += kvm_create_max_vcpus
>  TEST_GEN_PROGS_aarch64 += steal_time
> +TEST_GEN_PROGS_aarch64 += mem_slot_test
>  

kvm selftests has a bad case of OCD when it comes to lists of tests. In
the .gitignore and the Makefile we keep our tests in alphabetical order.
Maybe we should stop, because it's a bit annoying to maintain, but my
personal OCD won't allow it to be on my watch. Please fix the above
three lists.

>  TEST_GEN_PROGS_s390x = s390x/memop
>  TEST_GEN_PROGS_s390x += s390x/resets
> @@ -46,6 +48,7 @@ TEST_GEN_PROGS_s390x += s390x/sync_regs_test
>  TEST_GEN_PROGS_s390x += demand_paging_test
>  TEST_GEN_PROGS_s390x += dirty_log_test
>  TEST_GEN_PROGS_s390x += kvm_create_max_vcpus
> +TEST_GEN_PROGS_s390x += mem_slot_test
>  
>  TEST_GEN_PROGS += $(TEST_GEN_PROGS_$(UNAME_M))
>  LIBKVM += $(LIBKVM_$(UNAME_M))
> diff --git a/tools/testing/selftests/kvm/mem_slot_test.c b/tools/testing/selftests/kvm/mem_slot_test.c
> new file mode 100644
> index 000000000000..eef6f506f41d
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/mem_slot_test.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * mem_slot_test
> + *
> + * Copyright (C) 2020, Red Hat, Inc.
> + *
> + * Test suite for memory region operations.
> + */
> +#define _GNU_SOURCE /* for program_invocation_short_name */
> +#include <linux/kvm.h>
> +#include <sys/mman.h>
> +
> +#include "test_util.h"
> +#include "kvm_util.h"
> +
> +/*
> + * Test it can be added memory slots up to KVM_CAP_NR_MEMSLOTS, then any
> + * tentative to add further slots should fail.
> + */
> +static void test_add_max_slots(void)
> +{
> +	struct kvm_vm *vm;
> +	uint32_t max_mem_slots;
> +	uint32_t slot;
> +	uint64_t mem_reg_npages;
> +	uint64_t mem_reg_size;
> +	uint32_t mem_reg_flags;
> +	uint64_t guest_addr;
> +	int ret;
> +
> +	max_mem_slots = kvm_check_cap(KVM_CAP_NR_MEMSLOTS);
> +	TEST_ASSERT(max_mem_slots > 0,
> +		    "KVM_CAP_NR_MEMSLOTS should be greater than 0");
> +	pr_info("Allowed number of memory slots: %i\n", max_mem_slots);
> +
> +	vm = vm_create(VM_MODE_DEFAULT, 0, O_RDWR);
> +
> +	/*
> +	 * Uses 1MB sized/aligned memory region since this is the minimal
> +	 * required on s390x.
> +	 */
> +	mem_reg_size = 0x100000;
> +	mem_reg_npages = vm_calc_num_guest_pages(VM_MODE_DEFAULT, mem_reg_size);
> +
> +	mem_reg_flags = kvm_check_cap(KVM_CAP_READONLY_MEM) ? KVM_MEM_READONLY :
> +		KVM_MEM_LOG_DIRTY_PAGES;

I still don't see why we're setting a flag at all, and now we're setting
different flags depending on what's available, so the test isn't the
same for every environment. I would just have mem->flags = 0 for this
test.

> +
> +	guest_addr = 0x0;
> +
> +	/* Check it can be added memory slots up to the maximum allowed */
> +	pr_info("Adding slots 0..%i, each memory region with %ldK size\n",
> +		(max_mem_slots - 1), mem_reg_size >> 10);
> +	for (slot = 0; slot < max_mem_slots; slot++) {
> +		vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
> +					    guest_addr, slot, mem_reg_npages,
> +					    mem_reg_flags);
> +		guest_addr += mem_reg_size;
> +	}
> +
> +	/* Check it cannot be added memory slots beyond the limit */
> +	void *mem = mmap(NULL, mem_reg_size, PROT_READ | PROT_WRITE,
> +			 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +	TEST_ASSERT(mem != NULL, "Failed to mmap() host");

This should be testing mem != MAP_FAILED

> +
> +	struct kvm_userspace_memory_region kvm_region = {
> +		.slot = slot,
> +		.flags = mem_reg_flags,
> +		.guest_phys_addr = guest_addr,
> +		.memory_size = mem_reg_size,
> +		.userspace_addr = (uint64_t) mem,
> +	};

Declaring kvm_region in the middle of the block. I don't really care
myself, but it's inconsistent with all the other variables which are
declared at the top.

> +
> +	ret = ioctl(vm_get_fd(vm), KVM_SET_USER_MEMORY_REGION, &kvm_region);
> +	TEST_ASSERT(ret == -1, "Adding one more memory slot should fail");
> +	TEST_ASSERT(errno == EINVAL, "Should return EINVAL errno");

Please make the second assert message more specific. Or better would be
to combine the asserts

  TEST_ASSERT(ret == -1 && errno == EINVAL, "Adding one more memory slot should fail with EINVAL");

> +
> +	munmap(mem, mem_reg_size);
> +	kvm_vm_free(vm);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	test_add_max_slots();
> +	return 0;
> +}
> -- 
> 2.17.2
>

Thanks,
drew