linux-kernel - Re: [PATCH v2 4/4] vfio-pci: Best-effort huge pfnmaps with !MAP

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Message-ID: <202512051509.bh8Oncoq-lkp@intel.com>
Date: Fri, 5 Dec 2025 15:45:13 +0800
From: kernel test robot <lkp@...el.com>
To: Peter Xu <peterx@...hat.com>, kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	Jason Gunthorpe <jgg@...dia.com>, Nico Pache <npache@...hat.com>,
	Zi Yan <ziy@...dia.com>, Alex Mastro <amastro@...com>,
	David Hildenbrand <david@...hat.com>,
	Alex Williamson <alex@...zbot.org>, Zhi Wang <zhiw@...dia.com>,
	David Laight <david.laight.linux@...il.com>,
	Yi Liu <yi.l.liu@...el.com>, Ankit Agrawal <ankita@...dia.com>,
	peterx@...hat.com, Kevin Tian <kevin.tian@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v2 4/4] vfio-pci: Best-effort huge pfnmaps with
 !MAP_FIXED mappings

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@...el.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	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki