[PATCH] kvm: selftests: Introduce num-pages conversion utilities

[Andrew Jones <drjones@redhat.com>]

Guests and hosts don't have to have the same page size. This means
calculations are necessary when selecting the number of guest pages
to allocate in order to ensure the number is compatible with the
host. Provide utilities to help with those calculations.

Signed-off-by: Andrew Jones <drjones@redhat.com>
---
 tools/testing/selftests/kvm/dirty_log_test.c  |  3 +--
 .../testing/selftests/kvm/include/kvm_util.h  |  3 +++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 26 +++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 5614222a6628..c2bc4e4c91ec 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -295,8 +295,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
 	guest_num_pages = (guest_num_pages + 0xff) & ~0xffUL;
 #endif
 	host_page_size = getpagesize();
-	host_num_pages = (guest_num_pages * guest_page_size) / host_page_size +
-			 !!((guest_num_pages * guest_page_size) % host_page_size);
+	host_num_pages = vm_num_host_pages(vm, guest_num_pages);
 
 	if (!phys_offset) {
 		guest_test_phys_mem = (vm_get_max_gfn(vm) -
diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 29cccaf96baf..0d05ade3022c 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -158,6 +158,9 @@ unsigned int vm_get_page_size(struct kvm_vm *vm);
 unsigned int vm_get_page_shift(struct kvm_vm *vm);
 unsigned int vm_get_max_gfn(struct kvm_vm *vm);
 
+unsigned int vm_num_host_pages(struct kvm_vm *vm, unsigned int num_guest_pages);
+unsigned int vm_num_guest_pages(struct kvm_vm *vm, unsigned int num_host_pages);
+
 struct kvm_userspace_memory_region *
 kvm_userspace_memory_region_find(struct kvm_vm *vm, uint64_t start,
 				 uint64_t end);
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 41cf45416060..5af9d7b1b7fc 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -1667,3 +1667,29 @@ unsigned int vm_get_max_gfn(struct kvm_vm *vm)
 {
 	return vm->max_gfn;
 }
+
+static unsigned int vm_calc_num_pages(unsigned int num_pages,
+				      unsigned int page_shift,
+				      unsigned int new_page_shift)
+{
+	unsigned int n = 1 << (new_page_shift - page_shift);
+
+	if (page_shift >= new_page_shift)
+		return num_pages * (1 << (page_shift - new_page_shift));
+
+	return num_pages / n + !!(num_pages % n);
+}
+
+unsigned int vm_num_host_pages(struct kvm_vm *vm, unsigned int num_guest_pages)
+{
+	return vm_calc_num_pages(num_guest_pages,
+				 vm_get_page_shift(vm),
+				 __builtin_ffs(getpagesize()) - 1);
+}
+
+unsigned int vm_num_guest_pages(struct kvm_vm *vm, unsigned int num_host_pages)
+{
+	return vm_calc_num_pages(num_host_pages,
+				 __builtin_ffs(getpagesize()) - 1,
+				 vm_get_page_shift(vm));
+}
-- 
2.21.1