> -----Original Message-----
> From: Alex Williamson <[email protected]>
> Sent: Saturday, August 29, 2026 3:24 AM
> To: Manish Honap <[email protected]>
> Cc: [email protected]; Ankit Agrawal <[email protected]>; [email protected];
> [email protected]; [email protected]; Srirangan Madhavan
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; Yishai Hadas
> <[email protected]>; Shameer Kolothum Thodi
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; Neo Jia
> <[email protected]>; Krishnakant Jaju <[email protected]>; Vikram Sethi
> <[email protected]>; Zhi Wang <[email protected]>; linux-
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; linux-
> [email protected]; [email protected]; [email protected]
> Subject: Re: [PATCH v4 22/27] vfio/cxl: Revoke the HDM mapping on reset and
> power transitions
>
> External email: Use caution opening links or attachments
>
>
> 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
Agree. I will align it with the dma-buf direction. Kernel-v5 will add a dma-buf
export
of the HDM region (imported by iommufd) and revoke it on reset via move_notify.
I will coordinate with Matt to resolve this conflict.
Manish
>
> [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;
