[PATCH v12 1/4] selftests/vfio: Add memcpy chunking to vfio_pci_driver_memcpy()

[Rubin Du <rubind@nvidia.com>]

Add a chunking loop to vfio_pci_driver_memcpy() so that it breaks up
large memcpy requests into max_memcpy_size-sized chunks. This allows
callers to request any size without worrying about per-driver limits.
The memcpy_start()/memcpy_wait() semantics are unchanged.

Update the test to use 4x max_memcpy_size so it exercises the new
chunking path (4 iterations) while keeping execution fast for drivers
with small DMA transfer sizes.

Signed-off-by: Rubin Du <rubind@nvidia.com>
---
 .../selftests/vfio/lib/vfio_pci_driver.c       | 18 ++++++++++++++++--
 .../selftests/vfio/vfio_pci_driver_test.c      | 18 ++++++++++--------
 2 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_driver.c b/tools/testing/selftests/vfio/lib/vfio_pci_driver.c
index 6827f4a6febe..e6c5b9c703f4 100644
--- a/tools/testing/selftests/vfio/lib/vfio_pci_driver.c
+++ b/tools/testing/selftests/vfio/lib/vfio_pci_driver.c
@@ -106,7 +106,21 @@ int vfio_pci_driver_memcpy_wait(struct vfio_pci_device *device)
 int vfio_pci_driver_memcpy(struct vfio_pci_device *device,
 			   iova_t src, iova_t dst, u64 size)
 {
-	vfio_pci_driver_memcpy_start(device, src, dst, size, 1);
+	struct vfio_pci_driver *driver = &device->driver;
+	u64 offset = 0;
+
+	while (offset < size) {
+		u64 chunk = min(size - offset, driver->max_memcpy_size);
+		int ret;
+
+		vfio_pci_driver_memcpy_start(device, src + offset,
+					     dst + offset, chunk, 1);
+		ret = vfio_pci_driver_memcpy_wait(device);
+		if (ret)
+			return ret;
+
+		offset += chunk;
+	}
 
-	return vfio_pci_driver_memcpy_wait(device);
+	return 0;
 }
diff --git a/tools/testing/selftests/vfio/vfio_pci_driver_test.c b/tools/testing/selftests/vfio/vfio_pci_driver_test.c
index afa0480ddd9b..44aa90ee113a 100644
--- a/tools/testing/selftests/vfio/vfio_pci_driver_test.c
+++ b/tools/testing/selftests/vfio/vfio_pci_driver_test.c
@@ -89,12 +89,12 @@ FIXTURE_SETUP(vfio_pci_driver_test)
 	self->msi_fd = self->device->msi_eventfds[driver->msi];
 
 	/*
-	 * Use the maximum size supported by the device for memcpy operations,
-	 * slimmed down to fit into the memcpy region (divided by 2 so src and
-	 * dst regions do not overlap).
+	 * Use 4x the driver's max_memcpy_size to exercise the chunking
+	 * logic in vfio_pci_driver_memcpy(). Cap to half the memcpy
+	 * region so src and dst do not overlap.
 	 */
-	self->size = self->device->driver.max_memcpy_size;
-	self->size = min(self->size, self->memcpy_region.size / 2);
+	self->size = min_t(u64, driver->max_memcpy_size * 4,
+			   self->memcpy_region.size / 2);
 
 	self->src = self->memcpy_region.vaddr;
 	self->dst = self->src + self->size;
@@ -211,6 +211,7 @@ TEST_F_TIMEOUT(vfio_pci_driver_test, memcpy_storm, 60)
 {
 	struct vfio_pci_driver *driver = &self->device->driver;
 	u64 total_size;
+	u64 size;
 	u64 count;
 
 	fcntl_set_nonblock(self->msi_fd);
@@ -221,13 +222,14 @@ TEST_F_TIMEOUT(vfio_pci_driver_test, memcpy_storm, 60)
 	 * will take too long.
 	 */
 	total_size = 250UL * SZ_1G;
-	count = min(total_size / self->size, driver->max_memcpy_count);
+	size = min(driver->max_memcpy_size, self->memcpy_region.size / 2);
+	count = min(total_size / size, driver->max_memcpy_count);
 
-	printf("Kicking off %lu memcpys of size 0x%lx\n", count, self->size);
+	printf("Kicking off %lu memcpys of size 0x%lx\n", count, size);
 	vfio_pci_driver_memcpy_start(self->device,
 				     self->src_iova,
 				     self->dst_iova,
-				     self->size, count);
+				     size, count);
 
 	ASSERT_EQ(0, vfio_pci_driver_memcpy_wait(self->device));
 	ASSERT_NO_MSI(self->msi_fd);
-- 
2.43.0