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Message-ID: <20260107-scratch-amastro-vfio-dma-mapping-mmio-test-v1-1-0cec5e9ec89b@fb.com>
Date: Wed, 7 Jan 2026 14:13:28 -0800
From: Alex Mastro <amastro@...com>
To: Alex Williamson <alex@...zbot.org>, David Matlack <dmatlack@...gle.com>,
Shuah Khan <shuah@...nel.org>
CC: Peter Xu <peterx@...hat.com>, <linux-kernel@...r.kernel.org>,
<kvm@...r.kernel.org>, <linux-kselftest@...r.kernel.org>,
Jason Gunthorpe
<jgg@...pe.ca>, Alex Mastro <amastro@...com>
Subject: [PATCH] vfio: selftests: Add vfio_dma_mapping_mmio_test
Test MMIO-backed DMA mappings by iommu_map()-ing mmap'ed BAR regions.
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. 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@...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);
+
+ 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);
}
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;
+
+ 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, \
+}
+
+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);
+
+ 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, ®ion);
+ iommu_unmap(self->iommu, ®ion);
+}
+
+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, ®ion);
+ iommu_unmap(self->iommu, ®ion);
+}
+
+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@...com>
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