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Andrew Morton foundation.org>; Bjorn Helgaas ; Christian K=F6nig > ; dri-devel@lists.freedesktop.org; > iommu@lists.linux.dev; Jens Axboe ; Joerg Roedel > ; kvm@vger.kernel.org; linaro-mm-sig@lists.linaro.org; > linux-block@vger.kernel.org; linux-kernel@vger.kernel.org; linux- > media@vger.kernel.org; linux-mm@kvack.org; linux-pci@vger.kernel.org; > Logan Gunthorpe ; Marek Szyprowski > ; Robin Murphy ; > Sumit Semwal ; Vivek Kasireddy > ; Will Deacon > Subject: Re: [PATCH v4 10/10] vfio/pci: Add dma-buf export support for > MMIO regions >=20 > External email: Use caution opening links or attachments >=20 >=20 > On Mon, Sep 29, 2025 at 03:17:49PM -0600, Alex Williamson wrote: > > On Sun, 28 Sep 2025 17:50:20 +0300 > > Leon Romanovsky wrote: > > > +static int validate_dmabuf_input(struct vfio_pci_core_device *vdev, > > > + struct vfio_device_feature_dma_buf *dma_= buf, > > > + struct vfio_region_dma_range *dma_ranges= , > > > + struct p2pdma_provider **provider) > > > +{ > > > + struct pci_dev *pdev =3D vdev->pdev; > > > + u32 bar =3D dma_buf->region_index; > > > + resource_size_t bar_size; > > > + u64 sum; > > > + int i; > > > + > > > + if (dma_buf->flags) > > > + return -EINVAL; > > > + /* > > > + * For PCI the region_index is the BAR number like everything el= se. > > > + */ > > > + if (bar >=3D VFIO_PCI_ROM_REGION_INDEX) > > > + return -ENODEV; > > > + > > > + *provider =3D pcim_p2pdma_provider(pdev, bar); > > > + if (!provider) > > > > This needs to be IS_ERR_OR_NULL() or the function needs to settle on a > > consistent error return value regardless of CONFIG_PCI_P2PDMA. >=20 > pcim_p2pdma_provider() doesn't return errors after split to _init() and _= get(). > The more accurate check needs to be if (!*provider) and not what is writt= en. >=20 > > > > > + return -EINVAL; > > > + > > > + bar_size =3D pci_resource_len(pdev, bar); > > > > We get to this feature via vfio_pci_core_ioctl_feature(), which is used > > by several variant drivers, some of which mangle the BAR size exposed > > to the user, ex. hisi_acc. I'm afraid this might actually be giving > > dmabuf access to a portion of the BAR that isn't exposed otherwise. >=20 > Doe you mean that part? >=20 > 1185 static int hisi_acc_vf_qm_init(struct hisi_acc_vf_core_device > *hisi_acc_vdev) > 1186 { > ... > 1204 * Also the HiSilicon ACC VF devices supported by this dri= ver on > 1205 * HiSilicon hardware platforms are integrated end point d= evices > 1206 * and the platform lacks the capability to perform any PC= Ie P2P > 1207 * between these devices. > 1208 */ > 1209 > 1210 vf_qm->io_base =3D > 1211 ioremap(pci_resource_start(vf_dev, > VFIO_PCI_BAR2_REGION_INDEX), > 1212 pci_resource_len(vf_dev, > VFIO_PCI_BAR2_REGION_INDEX)); > 1213 if (!vf_qm->io_base) > 1214 return -EIO; > 1215 This is where hisi_acc reports a different BAR size as it tries to hide the migration control region from Guest access. static long hisi_acc_vfio_pci_ioctl(struct vfio_device *core_vdev, unsigned= int cmd, unsigned long arg) { ... if (info.index =3D=3D VFIO_PCI_BAR2_REGION_INDEX) { info.offset =3D VFIO_PCI_INDEX_TO_OFFSET(info.index); /* * ACC VF dev BAR2 region consists of both functional * register space and migration control register space. * Report only the functional region to Guest. */ info.size =3D pci_resource_len(pdev, info.index) / 2; info.flags =3D VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_WRITE | VFIO_REGION_INFO_FLAG_MMAP; return copy_to_user((void __user *)arg, &info, minsz) ? -EFAULT : 0; } } return vfio_pci_core_ioctl(core_vdev, cmd, arg); } > According to the comment, it doesn't support p2p and in any case we will > fail that platform in vfio_pci_dma_buf_attach() by taking "default" case: Yes. No P2P for this device. But variant drivers can override size exposed = to userspace like this one. Thanks, Shameer=20