From: Jason Gunthorpe <jgg@nvidia.com>
To: Matt Evans <matt@ozlabs.org>
Cc: "Pranjal Shrivastava" <praan@google.com>,
"Alex Williamson" <alex@shazbot.org>,
"Leon Romanovsky" <leon@kernel.org>,
"Alex Mastro" <amastro@fb.com>,
"Christian König" <christian.koenig@amd.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Logan Gunthorpe" <logang@deltatee.com>,
"Kevin Tian" <kevin.tian@intel.com>,
"Longfang Liu" <liulongfang@huawei.com>,
"Mahmoud Adam" <mngyadam@amazon.de>,
"David Matlack" <dmatlack@google.com>,
"Björn Töpel" <bjorn@kernel.org>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Ankit Agrawal" <ankita@nvidia.com>,
"Alistair Popple" <apopple@nvidia.com>,
"Vivek Kasireddy" <vivek.kasireddy@intel.com>,
linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
kvm@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH v5 3/9] vfio/pci: Add a helper to look up PFNs for DMABUFs
Date: Tue, 4 Aug 2026 21:41:37 -0300 [thread overview]
Message-ID: <20260805004137.GL27883@nvidia.com> (raw)
In-Reply-To: <cfae30ec-18ed-4f06-bf96-ef294a8c2744@ozlabs.org>
On Mon, Aug 03, 2026 at 07:22:06PM +0100, Matt Evans wrote:
> The second problem is this isn't just a limitation to not do an mmap()
> with offset approaching 1TB, because you could run into trouble just
> mapping, say, a 2TB BAR and then splitting it by unmapping a hole in the
> middle: the second VMA now has a huge offset.
>
> It seems a proper fix is easy though:
>
> unsigned long vma_off = (vma->vm_pgoff - priv->vma_pgoff_adjust) <<
> PAGE_SHIFT; /* No masking! */
>
> Then in vfio_pci_core_mmap_prep_dmabuf(),
>
> priv->vma_pgoff_adjust = vma->vm_pgoff;
>
> I.e., if vma_pgoff_adjust just includes the region index up high, it
> cancels out the (same) index in the vm_pgoff. Thus regular mmap should
> work (up to the 1TB offset), and DMABUF VMAs can have arbitrarily large
> offsets.
This is what I was expecting when I pointed at this stuff in the first
place :)
Jason
next prev parent reply other threads:[~2026-08-05 0:41 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-15 17:47 [PATCH v5 0/9] vfio/pci: Add mmap() for DMABUFs Matt Evans
2026-07-15 17:47 ` [PATCH v5 1/9] PCI/P2PDMA: Split pool-related cleanup out of pci_p2pdma_release() Matt Evans
2026-07-15 18:05 ` sashiko-bot
2026-07-17 8:02 ` Tian, Kevin
2026-07-28 22:33 ` Alex Williamson
2026-07-29 10:08 ` Leon Romanovsky
2026-08-05 0:31 ` Jason Gunthorpe
2026-07-30 16:45 ` Pranjal Shrivastava
2026-07-15 17:47 ` [PATCH v5 2/9] PCI/P2PDMA: Add CONFIG_PCI_P2PDMA_CORE Matt Evans
2026-07-15 18:03 ` sashiko-bot
2026-07-17 8:02 ` Tian, Kevin
2026-07-30 19:37 ` Pranjal Shrivastava
2026-08-04 15:42 ` Matt Evans
2026-08-04 16:19 ` Logan Gunthorpe
2026-08-05 0:39 ` Jason Gunthorpe
2026-08-05 16:28 ` Matt Evans
2026-08-05 16:40 ` Jason Gunthorpe
2026-08-05 20:50 ` Logan Gunthorpe
2026-07-15 17:47 ` [PATCH v5 3/9] vfio/pci: Add a helper to look up PFNs for DMABUFs Matt Evans
2026-07-15 18:08 ` sashiko-bot
2026-07-17 8:02 ` Tian, Kevin
2026-07-29 17:52 ` Alex Williamson
2026-07-30 17:34 ` Matt Evans
2026-07-30 22:55 ` Pranjal Shrivastava
2026-07-31 17:43 ` Matt Evans
2026-08-03 18:22 ` Matt Evans
2026-08-04 19:01 ` Pranjal Shrivastava
2026-08-05 0:41 ` Jason Gunthorpe [this message]
2026-07-15 17:47 ` [PATCH v5 4/9] vfio/pci: Add a helper to create a DMABUF for a BAR-map VMA Matt Evans
2026-07-15 18:12 ` sashiko-bot
2026-07-27 13:45 ` Matt Evans
2026-07-15 17:47 ` [PATCH v5 5/9] vfio/pci: Convert BAR mmap() to use a DMABUF Matt Evans
2026-07-15 18:13 ` sashiko-bot
2026-07-27 13:45 ` Matt Evans
2026-07-15 17:47 ` [PATCH v5 6/9] vfio/pci: Provide a user-facing name for BAR mappings Matt Evans
2026-07-15 18:01 ` sashiko-bot
2026-07-17 8:03 ` Tian, Kevin
2026-07-29 17:52 ` Alex Williamson
2026-07-30 14:37 ` Matt Evans
2026-07-15 17:47 ` [PATCH v5 7/9] vfio/pci: Clean up BAR zap and revocation Matt Evans
2026-07-15 18:00 ` sashiko-bot
2026-07-17 8:03 ` Tian, Kevin
2026-07-29 17:52 ` Alex Williamson
2026-07-30 14:47 ` Matt Evans
2026-08-04 20:10 ` Alex Williamson
2026-08-05 13:58 ` Matt Evans
2026-07-30 23:20 ` Pranjal Shrivastava
2026-07-15 17:47 ` [PATCH v5 8/9] vfio/pci: Support mmap() of a VFIO DMABUF Matt Evans
2026-07-15 18:17 ` sashiko-bot
2026-07-17 8:03 ` Tian, Kevin
2026-07-30 23:33 ` Pranjal Shrivastava
2026-07-15 17:47 ` [PATCH v5 9/9] vfio/pci: Permanently revoke a DMABUF on request Matt Evans
2026-07-15 18:11 ` sashiko-bot
2026-07-27 13:45 ` Matt Evans
2026-07-17 8:03 ` Tian, Kevin
2026-07-30 23:43 ` Pranjal Shrivastava
2026-07-15 18:12 ` [PATCH v5 0/9] vfio/pci: Add mmap() for DMABUFs David Matlack
2026-07-16 14:51 ` Matt Evans
2026-07-16 21:23 ` David Matlack
2026-07-17 8:42 ` David Laight
2026-07-17 16:30 ` David Matlack
2026-07-17 17:12 ` Matt Evans
2026-07-20 21:50 ` David Matlack
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