[PATCH v4 22/27] vfio/cxl: Revoke the HDM mapping on reset and power transitions

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.

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;
-- 
2.25.1