Re: [PATCH v2 4/4] vfio-pci: Best-effort huge pfnmaps with !MAP_FIXED mappings

kernel test robot
2025-12-05T07:45:42Z

Hi Peter,

kernel test robot noticed the following build warnings:

[auto build test WARNING on awilliam-vfio/for-linus]
[also build test WARNING on v6.18]
[cannot apply to akpm-mm/mm-everything awilliam-vfio/next brauner-vfs/vfs.all linus/master next-20251205]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url: https://github.com/intel-lab-lkp/linux/commits/Peter-Xu/mm-thp-Allow-thp_get_unmapped_area_vmflags-to-take-alignment/20251204-231258
base: https://github.com/awilliam/linux-vfio.git for-linus
patch link: https://lore.kernel.org/r/20251204151003.171039-5-peterx%40redhat.com
patch subject: [PATCH v2 4/4] vfio-pci: Best-effort huge pfnmaps with !MAP_FIXED mappings
config: i386-randconfig-006-20251205 (https://download.01.org/0day-ci/archive/20251205/202512051509.bh8Oncoq-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251205/202512051509.bh8Oncoq-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512051509.bh8Oncoq-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/vfio/pci/vfio_pci_core.c:1670:44: warning: shift count >= width of type [-Wshift-count-overflow]
1670 | req_start = (pgoff << PAGE_SHIFT) & ((1UL << VFIO_PCI_OFFSET_SHIFT) - 1);
| ^ ~~~~~~~~~~~~~~~~~~~~~
1 warning generated.

vim +1670 drivers/vfio/pci/vfio_pci_core.c

1642
1643 /*
1644 * Hint function for mmap() about the size of mapping to be carried out.
1645 * This helps to enable huge pfnmaps as much as possible on BAR mappings.
1646 *
1647 * This function does the minimum check on mmap() parameters to make the
1648 * hint valid only. The majority of mmap() sanity check will be done later
1649 * in mmap().
1650 */
1651 int vfio_pci_core_get_mapping_order(struct vfio_device *device,
1652 unsigned long pgoff, size_t len)
1653 {
1654 struct vfio_pci_core_device *vdev =
1655 container_of(device, struct vfio_pci_core_device, vdev);
1656 struct pci_dev *pdev = vdev->pdev;
1657 unsigned int index = pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
1658 unsigned long req_start;
1659 size_t phys_len;
1660
1661 /* Currently, only bars 0-5 supports huge pfnmap */
1662 if (index >= VFIO_PCI_ROM_REGION_INDEX)
1663 return 0;
1664
1665 /*
1666 * NOTE: we're keeping things simple as of now, assuming the
1667 * physical address of BARs (aka, pci_resource_start(pdev, index))
1668 * should always be aligned with pgoff in vfio-pci's address space.
1669 */
> 1670 req_start = (pgoff << PAGE_SHIFT) & ((1UL << VFIO_PCI_OFFSET_SHIFT) - 1);
1671 phys_len = PAGE_ALIGN(pci_resource_len(pdev, index));
1672
1673 /*
1674 * If this happens, it will probably fail mmap() later.. mapping
1675 * hint isn't important anymore.
1676 */
1677 if (req_start >= phys_len)
1678 return 0;
1679
1680 phys_len = MIN(phys_len - req_start, len);
1681
1682 if (IS_ENABLED(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP) && phys_len >= PUD_SIZE)
1683 return PUD_ORDER;
1684
1685 if (IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP) && phys_len >= PMD_SIZE)
1686 return PMD_ORDER;
1687
1688 return 0;
1689 }
1690 EXPORT_SYMBOL_GPL(vfio_pci_core_get_mapping_order);
1691

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