On Thu, 13 Aug 2026 15:06:26 +0530 <[email protected]> wrote: > From: Manish Honap <[email protected]> > > The HDM region is a device region, not a BAR, so vfio_pci_zap_bars() > leaves its PTEs in place. A runtime-PM entry, a D3 transition, or a reset > would then leave the guest with live mappings into a quiesced device. > > Add a zap hook, called alongside the BAR zap under memory_lock, that > unmaps the window. The fault path already refuses to re-insert PFNs while > the device is suspended or its Memory Space is disabled.
We need to think about what happens in the dmabuf mmap world[1]. Currently there are no device specific regions supporting mmap. Zapping is left as a compatibility interface, but the right solution is probably to use dmabuf for mmap where we can. Otherwise zap should likely be handled generically for device specific regions supporting mmap rather than as a CXL one-off. AFAIK, Matt's series is still in the works and this will conflict. Thanks, Alex [1]https://lore.kernel.org/all/[email protected]/ > Signed-off-by: Manish Honap <[email protected]> > --- > drivers/vfio/pci/cxl/vfio_cxl_core.c | 29 ++++++++++++++++++++++++++++ > drivers/vfio/pci/vfio_pci_core.c | 8 ++++++++ > include/linux/vfio_pci_core.h | 2 ++ > 3 files changed, 39 insertions(+) > > diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c > b/drivers/vfio/pci/cxl/vfio_cxl_core.c > index 0fb5ed5d86b7..f1c6bf06c408 100644 > --- a/drivers/vfio/pci/cxl/vfio_cxl_core.c > +++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c > @@ -530,6 +530,31 @@ static void vfio_cxl_release_device(struct > vfio_pci_core_device *vdev) > vdev->cxl = NULL; > } > > +static void vfio_cxl_zap(struct vfio_pci_core_device *vdev) > +{ > + struct vfio_cxl_state *cxl = vdev->cxl; > + > + lockdep_assert_held_write(&vdev->memory_lock); > + > + if (!cxl) > + return; > + > + /* > + * Revoke the mapping so a later access re-faults. Do not touch > hdm_valid > + * here: zap also runs on a plain PCI Memory-Space disable, across which > + * the committed HDM decoder stays valid (CXL.mem is not gated by PCI > + * Memory-Space). hdm_valid tracks decoder validity and is cleared only > by > + * the paths that can leave the decoder unrestored (a failed reset or PM > + * restore). A reset or D3 transition holds memory_lock for write while > it > + * runs, so no fault races the revoke, and a runtime-suspended device is > + * caught by the pm_runtime_engaged check on the insert path. > + */ > + unmap_mapping_range(vdev->vdev.inode->i_mapping, > + VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_NUM_REGIONS + > + cxl->hdm_region_idx), > + range_len(&cxl->hpa_range), true); > +} > + > static int vfio_cxl_open_device(struct vfio_pci_core_device *vdev) > { > struct vfio_cxl_state *cxl = vdev->cxl; > @@ -594,6 +619,9 @@ static int vfio_cxl_open_device(struct > vfio_pci_core_device *vdev) > if (ret) > goto err_free_shadows; > > + /* Remember where the HDM region landed so it can be zapped by index. */ > + cxl->hdm_region_idx = vdev->num_regions - 1; > + > ret = vfio_pci_core_register_dev_region(vdev, VFIO_REGION_TYPE_CXL, > > VFIO_REGION_SUBTYPE_CXL_COMP_REGS, > &vfio_cxl_comp_regops, > cxl->hdm_len, > @@ -738,6 +766,7 @@ static const struct vfio_cxl_ops vfio_cxl_ops = { > .close_device = vfio_cxl_close_device, > .config_read = vfio_cxl_config_read, > .config_write = vfio_cxl_config_write, > + .zap = vfio_cxl_zap, > .owner = THIS_MODULE, > }; > > diff --git a/drivers/vfio/pci/vfio_pci_core.c > b/drivers/vfio/pci/vfio_pci_core.c > index 77f8f39dd670..1a54f15d1c2c 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -1832,6 +1832,14 @@ void vfio_pci_zap_and_down_write_memory_lock(struct > vfio_pci_core_device *vdev) > { > down_write(&vdev->memory_lock); > vfio_pci_zap_bars(vdev); > + /* > + * The HDM region lives in the device-region offset range that > + * vfio_pci_zap_bars() does not cover, so revoke it here too. Otherwise > + * a runtime-PM entry, D3 transition, or reset would leave the guest > + * with live mappings into a quiesced device. > + */ > + if (vdev->cxl_ops && vdev->cxl_ops->zap) > + vdev->cxl_ops->zap(vdev); > } > > u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev) > diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h > index 294e95b5e881..8b93949d4484 100644 > --- a/include/linux/vfio_pci_core.h > +++ b/include/linux/vfio_pci_core.h > @@ -76,6 +76,8 @@ struct vfio_cxl_ops { > int count, __le32 *val); > int (*config_write)(struct vfio_pci_core_device *vdev, int pos, > int count, __le32 val); > + /* Revoke the HDM mapping; paired with the BAR zap */ > + void (*zap)(struct vfio_pci_core_device *vdev); > > /* Pinned per bound CXL device so vfio-cxl cannot unload under usage */ > struct module *owner;
