Re: [PATCH] vfio: selftests: Add vfio_dma_mapping_mmio_test

On 2026-01-07 02:13 PM, Alex Mastro wrote:

Test MMIO-backed DMA mappings by iommu_map()-ing mmap'ed BAR regions.

Thanks for adding this!

Also update vfio_pci_bar_map() to align BAR mmaps for efficient huge page mappings.

Only vfio_type1 variants are tested; iommufd variants can be added once kernel support lands.

Are there plans to support mapping BARs via virtual address in iommufd? I thought the plan was only to support via dma-bufs. Maybe Jason can confirm.

Assuming not, should we add negative tests here to make sure iommufd does not allow mapping BARs?

And then we can add dma-buf tests in a future commit.

The manual mmap alignment can be removed once mmap(!MAP_FIXED) on vfio device fds improves to automatically return well-aligned addresses.

Signed-off-by: Alex Mastro amastro@fb.com

Sanity test run:

$ ./vfio_dma_mapping_mmio_test 0000:05:00.0 TAP version 13 1..4 # Starting 4 tests from 2 test cases. # RUN vfio_dma_mapping_mmio_test.vfio_type1_iommu.map_full_bar ... Mapping BAR4: vaddr=0x7fad40000000 size=0x2000000000 iova=0x2000000000 # OK vfio_dma_mapping_mmio_test.vfio_type1_iommu.map_full_bar ok 1 vfio_dma_mapping_mmio_test.vfio_type1_iommu.map_full_bar # RUN vfio_dma_mapping_mmio_test.vfio_type1_iommu.map_partial_bar ... Mapping BAR4 (partial): vaddr=0x7fad40000000 size=0x1000 iova=0x0 # OK vfio_dma_mapping_mmio_test.vfio_type1_iommu.map_partial_bar ok 2 vfio_dma_mapping_mmio_test.vfio_type1_iommu.map_partial_bar # RUN vfio_dma_mapping_mmio_test.vfio_type1v2_iommu.map_full_bar ... Mapping BAR4: vaddr=0x7fad40000000 size=0x2000000000 iova=0x2000000000 # OK vfio_dma_mapping_mmio_test.vfio_type1v2_iommu.map_full_bar ok 3 vfio_dma_mapping_mmio_test.vfio_type1v2_iommu.map_full_bar # RUN vfio_dma_mapping_mmio_test.vfio_type1v2_iommu.map_partial_bar ... Mapping BAR4 (partial): vaddr=0x7fad40000000 size=0x1000 iova=0x0 # OK vfio_dma_mapping_mmio_test.vfio_type1v2_iommu.map_partial_bar ok 4 vfio_dma_mapping_mmio_test.vfio_type1v2_iommu.map_partial_bar # PASSED: 4 / 4 tests passed.

# Totals: pass:4 fail:0 xfail:0 xpass:0 skip:0 error:0

tools/testing/selftests/vfio/Makefile | 1 + tools/testing/selftests/vfio/lib/vfio_pci_device.c | 28 ++++- .../selftests/vfio/vfio_dma_mapping_mmio_test.c | 132 +++++++++++++++++++++ 3 files changed, 160 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vfio/Makefile b/tools/testing/selftests/vfio/Makefile index 3c796ca99a50..ead27892ab65 100644 --- a/tools/testing/selftests/vfio/Makefile +++ b/tools/testing/selftests/vfio/Makefile @@ -1,5 +1,6 @@ CFLAGS = $(KHDR_INCLUDES) TEST_GEN_PROGS += vfio_dma_mapping_test +TEST_GEN_PROGS += vfio_dma_mapping_mmio_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/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c index 13fdb4b0b10f..6f29543856a5 100644 --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c @@ -12,10 +12,13 @@ #include <sys/mman.h> #include <uapi/linux/types.h> +#include <linux/align.h> #include <linux/iommufd.h> +#include <linux/kernel.h> #include <linux/limits.h> #include <linux/mman.h> #include <linux/overflow.h> +#include <linux/sizes.h> #include <linux/types.h> #include <linux/vfio.h> @@ -124,20 +127,43 @@ static void vfio_pci_region_get(struct vfio_pci_device *device, int index, static void vfio_pci_bar_map(struct vfio_pci_device *device, int index) { struct vfio_pci_bar *bar = &device->bars[index];

• size_t align, size;
• void *map_base, *map_align; int prot = 0;

VFIO_ASSERT_LT(index, PCI_STD_NUM_BARS); VFIO_ASSERT_NULL(bar->vaddr); VFIO_ASSERT_TRUE(bar->info.flags & VFIO_REGION_INFO_FLAG_MMAP);

• VFIO_ASSERT_GT(bar->info.size, 0);

if (bar->info.flags & VFIO_REGION_INFO_FLAG_READ) prot |= PROT_READ; if (bar->info.flags & VFIO_REGION_INFO_FLAG_WRITE) prot |= PROT_WRITE;

• bar->vaddr = mmap(NULL, bar->info.size, prot, MAP_FILE | MAP_SHARED,

• /*

• * Align the mmap for more efficient IOMMU mapping.
  

• * The largest PUD size supporting huge pfnmap is 1GiB.
  

• */
  

• size = bar->info.size;
• align = min_t(u64, 1ULL << __builtin_ctzll(size), SZ_1G);

What's the reason to align to 1ULL << __builtin_ctzll(size) and not just size?

• map_base = mmap(NULL, size + align, PROT_NONE,

• 	MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  

• VFIO_ASSERT_NE(map_base, MAP_FAILED);
• map_align = (void *)ALIGN((uintptr_t)map_base, align);
• if (map_align > map_base)

• munmap(map_base, map_align - map_base);
  

• if (align > (size_t)(map_align - map_base))

• munmap(map_align + size, align - (map_align - map_base));
  

• bar->vaddr = mmap(map_align, size, prot, MAP_SHARED | MAP_FIXED, device->fd, bar->info.offset); VFIO_ASSERT_NE(bar->vaddr, MAP_FAILED);
• madvise(bar->vaddr, size, MADV_HUGEPAGE);

}

Can you split these changes out into a precursor commit? I think they stand on their own.

static void vfio_pci_bar_unmap(struct vfio_pci_device *device, int index) diff --git a/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c b/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c new file mode 100644 index 000000000000..211fa4203b49 --- /dev/null +++ b/tools/testing/selftests/vfio/vfio_dma_mapping_mmio_test.c @@ -0,0 +1,132 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include <stdio.h> +#include <sys/mman.h> +#include <unistd.h>

+#include <uapi/linux/types.h> +#include <linux/pci_regs.h> +#include <linux/sizes.h> +#include <linux/vfio.h>

+#include <libvfio.h>

+#include "../kselftest_harness.h"

+static const char *device_bdf;

+static int largest_mapped_bar(struct vfio_pci_device *device) +{

• int bar_idx = -1;
• u64 bar_size = 0;
• for (int i = 0; i < PCI_STD_NUM_BARS; i++) {

• struct vfio_pci_bar *bar = &device->bars[i];
  

• if (!bar->vaddr)
  

• 	continue;
  

• if (!(bar->info.flags & VFIO_REGION_INFO_FLAG_WRITE))
  

• 	continue;
  

nit: Add a comment here. I assume this is because iommu_map() tries to create writable IOMMU mappings?

Speaking of, maybe we can add a test that creating writable IOMMU mappings fails for read-only BARs?

• if (bar->info.size > bar_size) {
  

• 	bar_size = bar->info.size;
  

• 	bar_idx = i;
  

• }
  

• }
• return bar_idx;

+}

+FIXTURE(vfio_dma_mapping_mmio_test) {

• struct iommu *iommu;
• struct vfio_pci_device *device;
• struct iova_allocator *iova_allocator;
• int bar_idx;

+};

+FIXTURE_VARIANT(vfio_dma_mapping_mmio_test) {

• const char *iommu_mode;

+};

+#define FIXTURE_VARIANT_ADD_IOMMU_MODE(_iommu_mode) \ +FIXTURE_VARIANT_ADD(vfio_dma_mapping_mmio_test, _iommu_mode) { \

• .iommu_mode = #_iommu_mode, \

+}

nit: Alignment of trailing backslashes is off.

+FIXTURE_VARIANT_ADD_IOMMU_MODE(vfio_type1_iommu); +FIXTURE_VARIANT_ADD_IOMMU_MODE(vfio_type1v2_iommu);

+#undef FIXTURE_VARIANT_ADD_IOMMU_MODE

+FIXTURE_SETUP(vfio_dma_mapping_mmio_test) +{

• self->iommu = iommu_init(variant->iommu_mode);
• self->device = vfio_pci_device_init(device_bdf, self->iommu);
• self->iova_allocator = iova_allocator_init(self->iommu);
• self->bar_idx = largest_mapped_bar(self->device);

+}

+FIXTURE_TEARDOWN(vfio_dma_mapping_mmio_test) +{

• iova_allocator_cleanup(self->iova_allocator);
• vfio_pci_device_cleanup(self->device);
• iommu_cleanup(self->iommu);

+}

+TEST_F(vfio_dma_mapping_mmio_test, map_full_bar) +{

• struct vfio_pci_bar *bar;
• struct dma_region region;
• if (self->bar_idx < 0)

• SKIP(return, "No mappable BAR found on device %s", device_bdf);
  

I think you can do this in the FIXTURE_SETUP() to avoid duplication.

• bar = &self->device->bars[self->bar_idx];
• region = (struct dma_region) {

• .vaddr = bar->vaddr,
  

• .size = bar->info.size,
  

• .iova = iova_allocator_alloc(self->iova_allocator, bar->info.size),
  

• };
• printf("Mapping BAR%d: vaddr=%p size=0x%lx iova=0x%lx\n",

•       self->bar_idx, region.vaddr, region.size, region.iova);
  

• iommu_map(self->iommu, &region);
• iommu_unmap(self->iommu, &region);

+}

+TEST_F(vfio_dma_mapping_mmio_test, map_partial_bar) +{

• struct vfio_pci_bar *bar;
• struct dma_region region;
• size_t page_size;
• if (self->bar_idx < 0)

• SKIP(return, "No mappable BAR found on device %s", device_bdf);
  

• bar = &self->device->bars[self->bar_idx];
• page_size = getpagesize();
• if (bar->info.size < 2 * page_size)

• SKIP(return, "BAR%d too small for partial mapping test (size=0x%llx)",
  

•      self->bar_idx, bar->info.size);
  

• region = (struct dma_region) {

• .vaddr = bar->vaddr,
  

• .size = page_size,
  

• .iova = iova_allocator_alloc(self->iova_allocator, page_size),
  

• };
• printf("Mapping BAR%d (partial): vaddr=%p size=0x%lx iova=0x%lx\n",

•       self->bar_idx, region.vaddr, region.size, region.iova);
  

• iommu_map(self->iommu, &region);
• iommu_unmap(self->iommu, &region);

+}

+int main(int argc, char *argv[]) +{

• device_bdf = vfio_selftests_get_bdf(&argc, argv);
• return test_harness_run(argc, argv);

+}

---

base-commit: d721f52e31553a848e0e9947ca15a49c5674aef3 change-id: 20260107-scratch-amastro-vfio-dma-mapping-mmio-test-eecf25d9a742

Best regards,

Alex Mastro amastro@fb.com