Re: [PATCH] vfio: selftests: Add vfio_dma_mapping_mmio_test

[David Matlack <dmatlack@google.com>]

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>
>