Re: [PATCH 3/4] vfio: selftests: add iova allocator

On 2025-11-10 01:10 PM, Alex Mastro wrote:

Add struct iova_allocator, which gives tests a convenient way to generate legally-accessible IOVAs to map.

This is based on Alex Williamson's patch series for adding an IOVA allocator [1].

[1] https://lore.kernel.org/all/20251108212954.26477-1-alex@shazbot.org/

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

.../testing/selftests/vfio/lib/include/vfio_util.h | 14 +++++ tools/testing/selftests/vfio/lib/vfio_pci_device.c | 65 +++++++++++++++++++++- 2 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vfio/lib/include/vfio_util.h b/tools/testing/selftests/vfio/lib/include/vfio_util.h index fb5efec52316..bb1e7d39dfb9 100644 --- a/tools/testing/selftests/vfio/lib/include/vfio_util.h +++ b/tools/testing/selftests/vfio/lib/include/vfio_util.h @@ -13,6 +13,8 @@ #include "../../../kselftest.h" +#define ALIGN(x, a) (((x) + (a - 1)) & (~((a) - 1)))

Please name this ALIGN_UP() so that it is clear it aligns x up and not down.

#define VFIO_LOG_AND_EXIT(...) do { \ fprintf(stderr, " " __VA_ARGS__); \ fprintf(stderr, "\n"); \ @@ -188,6 +190,13 @@ struct vfio_pci_device { struct vfio_pci_driver driver; }; +struct iova_allocator {

• struct iommu_iova_range *ranges;
• size_t nranges;
• size_t range_idx;
• iova_t iova_next;

+};

/*

• Return the BDF string of the device that the test should use.

@@ -212,6 +221,11 @@ void vfio_pci_device_reset(struct vfio_pci_device *device); struct iommu_iova_range *vfio_pci_iova_ranges(struct vfio_pci_device *device, size_t *nranges); +int iova_allocator_init(struct vfio_pci_device *device,

• 	    struct iova_allocator *allocator);
  

+void iova_allocator_deinit(struct iova_allocator *allocator); +iova_t iova_allocator_alloc(struct iova_allocator *allocator, size_t size);

int __vfio_pci_dma_map(struct vfio_pci_device *device, struct vfio_dma_region *region); int __vfio_pci_dma_unmap(struct vfio_pci_device *device, diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c index 6bedbe65f0a1..a634feb1d378 100644 --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c @@ -12,11 +12,12 @@ #include <sys/mman.h> #include <uapi/linux/types.h> +#include <linux/iommufd.h> #include <linux/limits.h> #include <linux/mman.h> +#include <linux/overflow.h> #include <linux/types.h> #include <linux/vfio.h> -#include <linux/iommufd.h> #include "../../../kselftest.h" #include <vfio_util.h> @@ -190,6 +191,68 @@ struct iommu_iova_range *vfio_pci_iova_ranges(struct vfio_pci_device *device, return ranges; } +int iova_allocator_init(struct vfio_pci_device *device,

• 	struct iova_allocator *allocator)
  

+{

• struct iommu_iova_range *ranges;
• size_t nranges;
• memset(allocator, 0, sizeof(*allocator));
• ranges = vfio_pci_iova_ranges(device, &nranges);
• if (!ranges)

• return -ENOENT;
  

• *allocator = (struct iova_allocator){

• .ranges = ranges,
  

• .nranges = nranges,
  

• .range_idx = 0,
  

• .iova_next = 0,
  

• };
• return 0;

+}

+void iova_allocator_deinit(struct iova_allocator *allocator) +{

• free(allocator->ranges);

+}

I think it would be good to be consistent about how the library hands out and initializes objects. e.g. For devices we have:

device = vfio_pci_device_init(...); vfio_pci_device_cleanup(device);

So for allocator it would be:

allocator = iova_allocator_init(); iova_allocator_cleanup(allocator);

It's a small thing, but this way users of the library can always work with pointers allocated by the library, there is a consistent meaning of *_init() functions, and one doesn't have to distinguish between *_deinit() and *_cleanup().

Forcing dynamic memory allocation is less efficient, but I think simplicity and consistency matters more when it comes to tests.

+iova_t iova_allocator_alloc(struct iova_allocator *allocator, size_t size) +{

• int idx = allocator->range_idx;
• struct iommu_iova_range *range = &allocator->ranges[idx];
• VFIO_ASSERT_LT(idx, allocator->nranges, "IOVA allocator out of space\n");
• VFIO_ASSERT_GT(size, 0, "Invalid size arg, zero\n");
• VFIO_ASSERT_EQ(size & (size - 1), 0, "Invalid size arg, non-power-of-2\n");

ALIGN() is what requires size to be a power of 2, so the assert should probably go inside that macro.

• for (;;) {

• iova_t iova, last;
  

• iova = ALIGN(allocator->iova_next, size);
  

• if (iova < allocator->iova_next || iova > range->last ||
  

•     check_add_overflow(iova, size - 1, &last) ||
  

•     last > range->last) {
  

• 	allocator->range_idx = ++idx;
  

• 	VFIO_ASSERT_LT(idx, allocator->nranges,
  

• 		       "Out of ranges for allocation\n");
  

• 	allocator->iova_next = (++range)->start;
  

• 	continue;
  

• }
  

• if (check_add_overflow(last, (iova_t)1, &allocator->iova_next) ||
  

•     allocator->iova_next > range->last) {
  

• 	allocator->range_idx = ++idx;
  

• 	if (idx < allocator->nranges)
  

• 		allocator->iova_next = (++range)->start;
  

• }
  

• return iova;
  

• }

I found this loop a bit hard to read. The if statements have 3-4 statements, and idx and range are managed deep in the loop. What about something like this? It also avoids the need to check for overflow (unless I missed something :).

diff --git a/tools/testing/selftests/vfio/lib/include/vfio_util.h b/tools/testing/selftests/vfio/lib/include/vfio_util.h index bb1e7d39dfb9..63fce0ffe287 100644 --- a/tools/testing/selftests/vfio/lib/include/vfio_util.h +++ b/tools/testing/selftests/vfio/lib/include/vfio_util.h @@ -193,8 +193,10 @@ struct vfio_pci_device { struct iova_allocator { struct iommu_iova_range *ranges; size_t nranges; + + /* The next range, and offset within it, from which to allocate. */ size_t range_idx; - iova_t iova_next; + iova_t range_offset; };

/* diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c b/tools/testing/selftests/vfio/lib/vfio_pci_device.c index a634feb1d378..5b85005c4544 100644 --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c @@ -207,7 +207,7 @@ int iova_allocator_init(struct vfio_pci_device *device, .ranges = ranges, .nranges = nranges, .range_idx = 0, - .iova_next = 0, + .range_offset = 0, };

return 0; @@ -220,37 +220,41 @@ void iova_allocator_deinit(struct iova_allocator *allocator)

iova_t iova_allocator_alloc(struct iova_allocator *allocator, size_t size) { - int idx = allocator->range_idx; - struct iommu_iova_range *range = &allocator->ranges[idx]; + int idx;

- VFIO_ASSERT_LT(idx, allocator->nranges, "IOVA allocator out of space\n"); VFIO_ASSERT_GT(size, 0, "Invalid size arg, zero\n"); VFIO_ASSERT_EQ(size & (size - 1), 0, "Invalid size arg, non-power-of-2\n");

- for (;;) { + for (idx = allocator->range_idx; idx < allocator->nranges; idx++) { + struct iommu_iova_range *range = &allocator->ranges[idx]; iova_t iova, last;

- iova = ALIGN(allocator->iova_next, size); + if (idx == allocator->range_idx) + iova = ALIGN(range->start + allocator->range_offset, size); + else + iova = ALIGN(range->start, size);

- if (iova < allocator->iova_next || iova > range->last || - check_add_overflow(iova, size - 1, &last) || - last > range->last) { - allocator->range_idx = ++idx; - VFIO_ASSERT_LT(idx, allocator->nranges, - "Out of ranges for allocation\n"); - allocator->iova_next = (++range)->start; + if (range->last - iova + 1 < size) continue; - }

- if (check_add_overflow(last, (iova_t)1, &allocator->iova_next) || - allocator->iova_next > range->last) { - allocator->range_idx = ++idx; - if (idx < allocator->nranges) - allocator->iova_next = (++range)->start; + /* + * Found a range to hold the allocation. Update the allocator + * for the next allocation. + */ + last = iova + (size - 1); + + if (last < range->last) { + allocator->range_idx = idx; + allocator->range_offset = last - range->start + 1; + } else { + allocator->range_idx = idx + 1; + allocator->range_offset = 0; }

return iova; } + + VFIO_FAIL("Failed to iova range of size 0x%lx\n", size); }

iova_t __to_iova(struct vfio_pci_device *device, void *vaddr)

+}

iova_t __to_iova(struct vfio_pci_device *device, void *vaddr) { struct vfio_dma_region *region;

-- 2.47.3