On 2026-01-13 03:08 PM, Alex Mastro wrote: > Update vfio_pci_bar_map() to align BAR mmaps for efficient huge page > mappings. The manual mmap alignment can be removed once mmap(!MAP_FIXED) > on vfio device fds improves to automatically return well-aligned > addresses.
Please also mention that you added MADV_HUGEPAGE and why, and that you dropped MAP_FILE (just mention that it was unnecessary in the first place). > > Signed-off-by: Alex Mastro <[email protected]> > --- > tools/testing/selftests/vfio/lib/include/libvfio.h | 9 ++++++++ > tools/testing/selftests/vfio/lib/libvfio.c | 25 > ++++++++++++++++++++++ > tools/testing/selftests/vfio/lib/vfio_pci_device.c | 24 ++++++++++++++++++++- > 3 files changed, 57 insertions(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/vfio/lib/include/libvfio.h > b/tools/testing/selftests/vfio/lib/include/libvfio.h > index 279ddcd70194..5ebf8503586e 100644 > --- a/tools/testing/selftests/vfio/lib/include/libvfio.h > +++ b/tools/testing/selftests/vfio/lib/include/libvfio.h > @@ -23,4 +23,13 @@ > const char *vfio_selftests_get_bdf(int *argc, char *argv[]); > char **vfio_selftests_get_bdfs(int *argc, char *argv[], int *nr_bdfs); > > +/* > + * Reserve virtual address space of size at an address satisfying > + * (vaddr % align) == offset. > + * > + * Returns the reserved vaddr. The caller is responsible for unmapping > + * the returned region. > + */ > +void *mmap_aligned(size_t size, size_t align, size_t offset); nit: Perhaps we should name this mmap_reserve()? The current name implies something is being mmap'ed. > + > #endif /* SELFTESTS_VFIO_LIB_INCLUDE_LIBVFIO_H */ > diff --git a/tools/testing/selftests/vfio/lib/libvfio.c > b/tools/testing/selftests/vfio/lib/libvfio.c > index a23a3cc5be69..4529bb1e69d1 100644 > --- a/tools/testing/selftests/vfio/lib/libvfio.c > +++ b/tools/testing/selftests/vfio/lib/libvfio.c > @@ -2,6 +2,9 @@ > > #include <stdio.h> > #include <stdlib.h> > +#include <sys/mman.h> > + > +#include <linux/align.h> > > #include "../../../kselftest.h" > #include <libvfio.h> > @@ -76,3 +79,25 @@ const char *vfio_selftests_get_bdf(int *argc, char *argv[]) > > return vfio_selftests_get_bdfs(argc, argv, &nr_bdfs)[0]; > } > + > +void *mmap_aligned(size_t size, size_t align, size_t offset) > +{ > + void *map_base, *map_align; > + size_t delta; > + > + VFIO_ASSERT_GT(align, offset); > + delta = align - offset; > + > + 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 + delta, align) - delta); > + > + if (map_align > map_base) > + VFIO_ASSERT_EQ(munmap(map_base, map_align - map_base), 0); > + > + VFIO_ASSERT_EQ(munmap(map_align + size, map_base + align - map_align), > 0); > + > + return map_align; > +} > diff --git a/tools/testing/selftests/vfio/lib/vfio_pci_device.c > b/tools/testing/selftests/vfio/lib/vfio_pci_device.c > index 13fdb4b0b10f..03f35011b5f7 100644 > --- a/tools/testing/selftests/vfio/lib/vfio_pci_device.c > +++ b/tools/testing/selftests/vfio/lib/vfio_pci_device.c > @@ -12,10 +12,14 @@ > #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/log2.h> > #include <linux/mman.h> > #include <linux/overflow.h> > +#include <linux/sizes.h> > #include <linux/types.h> > #include <linux/vfio.h> > > @@ -124,20 +128,38 @@ 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 *vaddr; > int prot = 0; uber-nit: Put vaddr after prot to preserve the reverse-fir-tree ordering of variables. Here's the tip tree documentation: https://docs.kernel.org/process/maintainer-tip.html#variable-declarations I should probably document somewhere that this is preferred in VFIO selftests as well. > > 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_TRUE(is_power_of_2(bar->info.size)); > > 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, > + size = bar->info.size; > + > + /* > + * Align BAR mmaps to improve page fault granularity during potential > + * subsequent IOMMU mapping of these BAR vaddr. 1G for x86 is the > + * largest hugepage size across any architecture, so no benefit from > + * larger alignment. BARs smaller than 1G will be aligned by their > + * power-of-two size, guaranteeing sufficient alignment for smaller > + * hugepages, if present. > + */ > + align = min_t(size_t, size, SZ_1G); > + > + vaddr = mmap_aligned(size, align, 0); > + bar->vaddr = mmap(vaddr, 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) > > -- > 2.47.3 >
