Re: [RFC PATCH 4/6] selftests/vfio: Exercise sPAPR DDW path for hugepage DMA mappings

[David Matlack <dmatlack@google.com>]

On 2026-07-06 10:33 PM, David Matlack wrote:
> On 2026-07-02 11:28 PM, Narayana Murty N wrote:
> > Prepare the DMA window before IOVA allocation in the DMA mapping tests.
> > 
> > Anonymous mappings use the default sPAPR DMA window. HugeTLB mappings force
> > a DDW with the requested page size, allowing the test to exercise DDW
> > creation, mapping, unmapping, and cleanup.
> > 
> > Skip gracefully when hugepage allocation fails or when the platform does
> > not support the requested DDW characteristics. Also skip unmap-all when
> > the backend cannot pair it with the sPAPR memory unregister flow.
> > 
> > Signed-off-by: Narayana Murty N <nnmlinux@linux.ibm.com>
> > ---
> >  .../selftests/vfio/vfio_dma_mapping_test.c    | 22 +++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/vfio/vfio_dma_mapping_test.c b/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> > index 7d0de8c79de1..4411fdbd56da 100644
> > --- a/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> > +++ b/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> > @@ -1,5 +1,6 @@
> >  // SPDX-License-Identifier: GPL-2.0-only
> >  #include <stdio.h>
> > +#include <string.h>
> >  #include <sys/mman.h>
> >  #include <unistd.h>
> >  
> > @@ -119,8 +120,19 @@ FIXTURE_VARIANT_ADD_ALL_IOMMU_MODES(anonymous_hugetlb_1gb, SZ_1G, MAP_HUGETLB |
> >  
> >  FIXTURE_SETUP(vfio_dma_mapping_test)
> >  {
> > +	const u64 page_size = variant->size ?: getpagesize();
> > +	const bool force_dynamic = !!variant->size;
> 
> This is kind of arbitrary right? Should we add explicit variants for
> dynamic/default windows (see below). But we need some way to skip the dynamic
> window tests on non-spapr iommus...

Maybe the flow can be something like this:

  iommu = iommu_init(); /* sets up default window */

  if (variant->dynamic_window) {
          ret = iommu_dma_window_create(...); /* always fails on non-sapr iommus */
          if (ret)
                  SKIP(...);
  }

Then I think you also want to add some call to gracefully skip tests if
the current window does not support the desired mapping. e.g.

  if (!iommu_dma_window_fits(region)) /* always succeeds on non-spapr iommus */
          SKIP(...);

> 
> diff --git a/tools/testing/selftests/vfio/vfio_dma_mapping_test.c b/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> index cd2d3276a46c..b54c529ebedb 100644
> --- a/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> +++ b/tools/testing/selftests/vfio/vfio_dma_mapping_test.c
> @@ -103,15 +103,21 @@ FIXTURE_VARIANT(vfio_dma_mapping_test) {
>         const char *iommu_mode;
>         u64 size;
>         int mmap_flags;
> +       bool dynamic_window;
>  };
> 
> -#define FIXTURE_VARIANT_ADD_IOMMU_MODE(_iommu_mode, _name, _size, _mmap_flags) \
> -FIXTURE_VARIANT_ADD(vfio_dma_mapping_test, _iommu_mode ## _ ## _name) {               \
> -       .iommu_mode = #_iommu_mode,                                            \
> -       .size = (_size),                                                       \
> -       .mmap_flags = MAP_ANONYMOUS | MAP_PRIVATE | (_mmap_flags),             \
> +#define __FIXTURE_VARIANT_ADD_IOMMU_MODE(_iommu_mode, _name, _size, _mmap_flags, _dynamic_window) \
> +FIXTURE_VARIANT_ADD(vfio_dma_mapping_test,_iommu_mode ## _ ## _name) {   \
> +       .iommu_mode = #_iommu_mode,                                                               \
> +       .size = (_size),                                                                          \
> +       .mmap_flags = MAP_ANONYMOUS | MAP_PRIVATE | (_mmap_flags),                                \
> +       .dynamic_window = _dynamic_window,                                                        \
>  }
> 
> +#define FIXTURE_VARIANT_ADD_IOMMU_MODE(_iommu_mode, _name, _size, _mmap_flags)  \
> +__FIXTURE_VARIANT_ADD_IOMMU_MODE(_iommu_mode, _name, _size, _mmap_flags, false); \
> +__FIXTURE_VARIANT_ADD_IOMMU_MODE(_iommu_mode, _name ## _dynamic_window, _size, _mmap_flags, true) \
> +
>  FIXTURE_VARIANT_ADD_ALL_IOMMU_MODES(anonymous, 0, 0);
>  FIXTURE_VARIANT_ADD_ALL_IOMMU_MODES(anonymous_hugetlb_2mb, SZ_2M, MAP_HUGETLB | MAP_HUGE_2MB);
>  FIXTURE_VARIANT_ADD_ALL_IOMMU_MODES(anonymous_hugetlb_1gb, SZ_1G, MAP_HUGETLB | MAP_HUGE_1GB);
> @@ -121,14 +127,13 @@ FIXTURE_VARIANT_ADD_ALL_IOMMU_MODES(anonymous_hugetlb_1gb, SZ_1G, MAP_HUGETLB |
>  FIXTURE_SETUP(vfio_dma_mapping_test)
>  {
>         const u64 page_size = variant->size ?: getpagesize();
> -       const bool force_dynamic = !!variant->size;
>         int ret;
> 
>         self->iommu = iommu_init(variant->iommu_mode);
>         self->device = vfio_pci_device_init(device_bdf, self->iommu);
> 
>         ret = iommu_prepare_dma_window(self->iommu, page_size, page_size,
> -                                      force_dynamic);
> +                                      variant->dynamic_window);
>         if (ret)
>                 SKIP(return, "DMA window unavailable: %s (%d)\n",
>                      strerror(-ret), -ret);
> 
> > +	int ret;
> > +
> >  	self->iommu = iommu_init(variant->iommu_mode);
> >  	self->device = vfio_pci_device_init(device_bdf, self->iommu);
> > +
> > +	ret = iommu_prepare_dma_window(self->iommu, page_size, page_size,
> > +				       force_dynamic);
> > +	if (ret)
> > +		SKIP(return, "DMA window unavailable: %s (%d)\n",
> > +		     strerror(-ret), -ret);
> > +
> >  	self->iova_allocator = iova_allocator_init(self->iommu);
> >  }
> >  
> > @@ -227,6 +239,7 @@ FIXTURE_SETUP(vfio_dma_map_limit_test)
> >  	u64 region_size = getpagesize();
> >  	iova_t last_iova;
> >  	u32 nranges;
> > +	int ret;
> >  
> >  	/*
> >  	 * Over-allocate mmap by double the size to provide enough backing vaddr
> > @@ -236,6 +249,13 @@ FIXTURE_SETUP(vfio_dma_map_limit_test)
> >  
> >  	self->iommu = iommu_init(variant->iommu_mode);
> >  	self->device = vfio_pci_device_init(device_bdf, self->iommu);
> > +
> > +	ret = iommu_prepare_dma_window(self->iommu, region_size, region_size,
> > +				       false);
> > +	if (ret)
> > +		SKIP(return, "DMA window unavailable: %s (%d)\n",
> > +		     strerror(-ret), -ret);
> > +
> >  	region->vaddr = mmap(NULL, self->mmap_size, PROT_READ | PROT_WRITE,
> >  			     MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> >  	ASSERT_NE(region->vaddr, MAP_FAILED);
> > @@ -277,6 +297,8 @@ TEST_F(vfio_dma_map_limit_test, unmap_all)
> >  	u64 unmapped;
> >  	int rc;
> >  
> > +	if (!iommu_supports_unmap_all(self->iommu))
> > +		SKIP(return, "IOMMU backend does not support unmap-all\n");
> >  	iommu_map(self->iommu, region);
> >  	ASSERT_EQ(region->iova, to_iova(self->device, region->vaddr));
> >  
> > -- 
> > 2.51.1
> >