From: Manish Honap <[email protected]> The HDM decoder register block lives in the component BAR that vfio-pci owns. The guest reads the decoder only through the trapped, read-only decoder region; it must not reach the physical registers through the BAR directly, and a write through the BAR could uncommit or move an unlocked decoder that the host relies on.
Add the block to the generic excluded-range list with VFIO_PCI_EXCLUDE_MMAP | VFIO_PCI_EXCLUDE_READ | VFIO_PCI_EXCLUDE_WRITE similar to the MSI-X exclusion. Assisted-by: LLM Signed-off-by: Manish Honap <[email protected]> --- drivers/vfio/pci/cxl/vfio_cxl_core.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c b/drivers/vfio/pci/cxl/vfio_cxl_core.c index 4a8aaa765a98..68e898ee1985 100644 --- a/drivers/vfio/pci/cxl/vfio_cxl_core.c +++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c @@ -614,6 +614,22 @@ static int vfio_cxl_open_device(struct vfio_pci_core_device *vdev) struct vfio_cxl_state *cxl = vdev->cxl; int ret; + /* + * Keep the HDM decoder block out of the guest's direct BAR access: the + * guest reaches it only through the trapped decoder region, and a write + * through the BAR could uncommit or move an unlocked decoder that the + * host relies on. Exclude it from mmap, fill reads with -1 and drop + * writes. The list is cleared on close, so re-add it per open. + */ + ret = vfio_pci_core_add_excluded_range(vdev, cxl->hdm->hdm_bar, + cxl->hdm->hdm_offset, + cxl->hdm_len, + VFIO_PCI_EXCLUDE_MMAP | + VFIO_PCI_EXCLUDE_READ | + VFIO_PCI_EXCLUDE_WRITE); + if (ret) + return ret; + /* * vfio-pci-core frees all dynamic regions on close and on a failed * open, so register them here per open rather than at bind. -- 2.53.0
