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vfio: selftests: Align BAR mmaps for efficient IOMMU mapping

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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.

Also add MADV_HUGEPAGE, which encourages the kernel to use huge pages
(e.g. when /sys/kernel/mm/transparent_hugepage/enabled is set to "madvise").

Drop MAP_FILE from mmap(). It is an ignored compatibility flag.

Signed-off-by: Alex Mastro <amastro@fb.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Tested-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20260114-map-mmio-test-v3-2-44e036d95e64@fb.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
This commit is contained in:
Alex Mastro
2026-01-14 10:57:17 -08:00
committed by Alex Williamson
parent 03b7c2d763
commit 557dbdf6c4
3 changed files with 57 additions and 1 deletions
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24
tools/testing/selftests/vfio/lib/vfio_pci_device.c
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@@ -11,10 +11,14 @@
#include <sys/ioctl.h>
#include <sys/mman.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>
@@ -123,20 +127,38 @@ 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;
int prot = 0;
void *vaddr;
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_reserve(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)