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Message-ID: <aRJtDHJZ6yAW2xIj@google.com>
Date: Mon, 10 Nov 2025 22:54:04 +0000
From: David Matlack <dmatlack@...gle.com>
To: Alex Mastro <amastro@...com>
Cc: Alex Williamson <alex@...zbot.org>, Shuah Khan <shuah@...nel.org>,
kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>
Subject: 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@...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
>
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