Re: [RFC PATCH 2/3] vfio: selftests: Add iommufd hwpt replace test

[Samiullah Khawaja <skhawaja@google.com>]

On Wed, Oct 21, 2026 at 10:39:34PM +0000, David Matlack wrote:
>On 2026-09-25 01:13 AM, Samiullah Khawaja wrote:
>> Add a test that does iommufd hwpt replace while a DMA is ongoing. This
>> verifies the hitless replace of IOMMU domain without disrupting the DMA.
>>
>> Note that the new domain is attached after mapping the required DMA
>> memory at the same IOVA in the new domain.
>>
>> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
>
>Aside from the MODE_IOMMUFD nit,
>
>Reviewed-by: David Matlack <dmatlack@google.com>
>
>> ---
>>  tools/testing/selftests/vfio/Makefile         |   1 +
>>  .../vfio/vfio_iommufd_hwpt_replace_test.c     | 171 ++++++++++++++++++
>>  2 files changed, 172 insertions(+)
>>  create mode 100644 tools/testing/selftests/vfio/vfio_iommufd_hwpt_replace_test.c
>>
>> diff --git a/tools/testing/selftests/vfio/Makefile b/tools/testing/selftests/vfio/Makefile
>> index 2c32c48db509..01d0e808871b 100644
>> --- a/tools/testing/selftests/vfio/Makefile
>> +++ b/tools/testing/selftests/vfio/Makefile
>> @@ -8,6 +8,7 @@ else
>>  CFLAGS = $(KHDR_INCLUDES)
>>  TEST_GEN_PROGS += vfio_dma_mapping_test
>>  TEST_GEN_PROGS += vfio_dma_mapping_mmio_test
>> +TEST_GEN_PROGS += vfio_iommufd_hwpt_replace_test
>>  TEST_GEN_PROGS += vfio_iommufd_setup_test
>>  TEST_GEN_PROGS += vfio_pci_device_test
>>  TEST_GEN_PROGS += vfio_pci_device_init_perf_test
>> diff --git a/tools/testing/selftests/vfio/vfio_iommufd_hwpt_replace_test.c b/tools/testing/selftests/vfio/vfio_iommufd_hwpt_replace_test.c
>> new file mode 100644
>> index 000000000000..3ec243aae626
>> --- /dev/null
>> +++ b/tools/testing/selftests/vfio/vfio_iommufd_hwpt_replace_test.c
>> @@ -0,0 +1,171 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +#include <string.h>
>> +#include <sys/ioctl.h>
>> +#include <sys/mman.h>
>> +
>> +#include <linux/sizes.h>
>> +#include <linux/vfio.h>
>> +
>> +#include <libvfio.h>
>> +
>> +#include "kselftest_harness.h"
>> +
>> +static const char *device_bdf;
>> +
>> +static void region_setup(struct iommu *iommu,
>> +			 struct iova_allocator *iova_allocator,
>> +			 struct dma_region *region, u64 size)
>> +{
>> +	const int flags = MAP_SHARED | MAP_ANONYMOUS;
>> +	const int prot = PROT_READ | PROT_WRITE;
>> +	void *vaddr;
>> +
>> +	vaddr = mmap(NULL, size, prot, flags, -1, 0);
>> +	VFIO_ASSERT_NE(vaddr, MAP_FAILED);
>> +
>> +	region->vaddr = vaddr;
>> +	region->iova = iova_allocator_alloc(iova_allocator, size);
>> +	region->size = size;
>> +
>> +	iommu_map(iommu, region);
>> +}
>> +
>> +static void region_teardown(struct iommu *iommu, struct dma_region *region)
>> +{
>> +	iommu_unmap(iommu, region);
>> +	VFIO_ASSERT_EQ(munmap(region->vaddr, region->size), 0);
>> +}
>> +
>> +FIXTURE(vfio_iommufd_replace_hwpt_test) {
>> +	struct iommu *iommu;
>> +	struct vfio_pci_device *device;
>> +	struct iova_allocator *iova_allocator;
>> +	struct dma_region memcpy_region;
>> +
>> +	u64 size;
>> +	void *src;
>> +	void *dst;
>> +	iova_t src_iova;
>> +	iova_t dst_iova;
>> +};
>> +
>> +FIXTURE_SETUP(vfio_iommufd_replace_hwpt_test)
>> +{
>> +	struct vfio_pci_driver *driver;
>> +
>> +	self->iommu = iommu_init("iommufd");
>
>nit: iommu_init(MODE_IOMMUFD)
>
>This needs to be fixed in iommufd_iommu_init() in the previous patch as
>well.
>
>> +	self->device = vfio_pci_device_init(device_bdf, self->iommu);
>> +	self->iova_allocator = iova_allocator_init(self->iommu);
>> +
>> +	driver = &self->device->driver;
>> +
>> +	region_setup(self->iommu, self->iova_allocator, &self->memcpy_region, SZ_2M);
>> +	region_setup(self->iommu, self->iova_allocator, &driver->region, SZ_2M);
>
>The driver->region.size is now populated automatically based on what the
>driver needs. So you can just pass in driver->region.size here instead
>of hard-coding SZ_2M.
>
>> +
>> +	if (driver->ops)
>> +		vfio_pci_driver_init(self->device);
>> +
>> +	self->size = self->memcpy_region.size / 2;
>> +	self->src = self->memcpy_region.vaddr;
>> +	self->dst = self->src + self->size;
>> +
>> +	self->src_iova = to_iova(self->device, self->src);
>> +	self->dst_iova = to_iova(self->device, self->dst);
>> +}
>> +
>> +FIXTURE_TEARDOWN(vfio_iommufd_replace_hwpt_test)
>> +{
>> +	struct vfio_pci_driver *driver = &self->device->driver;
>> +
>> +	if (driver->ops)
>> +		vfio_pci_driver_remove(self->device);
>> +
>> +	region_teardown(self->iommu, &self->memcpy_region);
>> +	region_teardown(self->iommu, &driver->region);
>> +
>> +	iova_allocator_cleanup(self->iova_allocator);
>> +	vfio_pci_device_cleanup(self->device);
>> +	iommu_cleanup(self->iommu);
>> +}
>> +
>> +FIXTURE_VARIANT(vfio_iommufd_replace_hwpt_test) {
>> +	u32 attaches;
>> +};
>> +
>> +FIXTURE_VARIANT_ADD(vfio_iommufd_replace_hwpt_test, domain_replace) {
>> +	.attaches = 1000,
>
>Maybe we should replace memcpy_wait() with memcpy_poll() and move the
>wait loop out into the generic driver layer (vfio_pci_driver.c)
>repeatedly calling memcpy_poll(). The would let you do replaces until
>the memcpy is done instead of hard-coding a random number, and also lift
>more code out of the the drivers and into the generic core.

The purpose of this being here was to a N number of attaches/replaces as
it might have chance to produce faults, as this is basically race. While
I agree poll() is a useful op to have, but in the context of this test
maybe it is an overkill.

Thanks,
Sami
>
>It should be easy enough to swap the drivers from wait() to poll() model
>if you are feeling up for it. Not a blocker for this series though.
>
>> +};
>> +
>> +FIXTURE_VARIANT_ADD(vfio_iommufd_replace_hwpt_test, noreplace) {
>> +	.attaches = 0,
>> +};
>> +
>> +TEST_F_TIMEOUT(vfio_iommufd_replace_hwpt_test, memcpy, 120)
>> +{
>> +	struct dma_region memcpy_region = {}, driver_region = {};
>> +	struct vfio_pci_driver *driver = &self->device->driver;
>> +	struct iommu *iommu2 = NULL;
>> +	u64 size = 0;
>> +	int ret;
>> +	u32 i;
>> +
>> +	if (variant->attaches) {
>> +		iommu2 = iommufd_iommu_init(self->iommu->iommufd,
>> +					    self->device->dev_id);
>> +
>> +		memcpy_region = self->memcpy_region;
>> +		driver_region = self->device->driver.region;
>> +
>> +		iommu_map(iommu2, &memcpy_region);
>> +		iommu_map(iommu2, &driver_region);
>> +	}
>> +
>> +	if (driver->ops) {
>> +		memset(self->src, 'x', self->size);
>> +		memset(self->dst, 'y', self->size);
>> +
>> +		size = min_t(u64, driver->max_memcpy_size, self->size);
>> +
>> +		/*
>> +		 * Fill the device's queue. memcpy_start() returns with
>> +		 * max_memcpy_count transfers still outstanding.
>> +		 */
>> +		vfio_pci_driver_memcpy_start(self->device,
>> +					     self->src_iova,
>> +					     self->dst_iova,
>> +					     size, driver->max_memcpy_count);
>> +	}
>> +
>> +	/*
>> +	 * Replace the domain repeatedly while that transfer is in flight. Since
>> +	 * domain replacement is a race with the translation requests, it needs
>> +	 * to be done multiple times to capture the small window where iommu
>> +	 * faults can occur.
>> +	 *
>> +	 * The loop ends on the original domain, so the teardown below is safe.
>> +	 */
>> +	for (i = 0; i < variant->attaches; i++) {
>> +		vfio_pci_device_attach_iommu(self->device, iommu2);
>> +		vfio_pci_device_attach_iommu(self->device, self->iommu);
>> +	}
>> +
>> +	if (driver->ops) {
>> +		ret = vfio_pci_driver_memcpy_wait(self->device);
>> +
>> +		ASSERT_EQ(0, ret);
>> +		ASSERT_EQ(0, memcmp(self->src, self->dst, size));
>> +	}
>> +
>> +	if (iommu2) {
>> +		iommu_unmap(iommu2, &memcpy_region);
>> +		iommu_unmap(iommu2, &driver_region);
>> +		iommu_cleanup(iommu2);
>> +	}
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +	device_bdf = vfio_selftests_get_bdf(&argc, argv);
>> +
>> +	return test_harness_run(argc, argv);
>> +}
>> --
>> 2.56.0.rc1.315.gc6ed9934b7-goog
>>