[PATCH v5 24/24] iommu/amd: Relocate vIOMMU translate-device-id on PCI reserve

[Suravee Suthikulpanit]

When PCI probe reserves a BDF already allocated to a vIOMMU, relocate
that vIOMMU to a newly allocated translate-device-id before marking the
BDF reserved for the device. Reserve holds the segment mutex and
trylocks trans_devid_lock so the vIOMMU pointer stays valid without
reversing the nested lock order. Reprogram translation DTE and VFctrl
under trans_devid_lock; roll back the pool on failure.

Mark from_id reserved with a raw xa_store so ALLOCATED->RESERVED does
not WARN on the non-NULL owner. On MMIO failure, restore from_id the
same way (RESERVED->owner) instead of install_allocated.

Reuse the vIOMMU's trans_dev_data object. After programming the new
slot, clear the old DTE without freeing the object.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 drivers/iommu/amd/amd_iommu_types.h |  10 +-
 drivers/iommu/amd/trans_devid.c     | 146 +++++++++++++++++++++++++++-
 2 files changed, 152 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index c748bab27509..347c6954439d 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -558,11 +558,15 @@ struct amd_iommu_viommu {
 
 	/*
 	 * Serializes this vIOMMU's translation DTE and VFctrl TransDevID
-	 * updates on init and teardown. VFctrl TransDevID is not written
-	 * from amd_viommu_uninit_one().
+	 * updates on init and teardown against PCI-probe relocation, which
+	 * may reprogram the same registers to a newly allocated id.
+	 * VFctrl TransDevID is not written from amd_viommu_uninit_one().
 	 *
 	 * Nested lock order: trans_devid_lock, then
-	 * pci_seg->trans_devid_mutex.
+	 * pci_seg->trans_devid_mutex (same as destroy). Relocate drops
+	 * the segment mutex around the MMIO updates. Reserve holds the
+	 * segment mutex and mutex_trylock()s trans_devid_lock so the
+	 * aviommu pointer stays valid without reversing lock order.
 	 */
 	struct mutex trans_devid_lock;
 
diff --git a/drivers/iommu/amd/trans_devid.c b/drivers/iommu/amd/trans_devid.c
index 3a4e09fe39d5..785f829db719 100644
--- a/drivers/iommu/amd/trans_devid.c
+++ b/drivers/iommu/amd/trans_devid.c
@@ -12,6 +12,7 @@
 
 #include <linux/kernel.h>
 #include <linux/pci.h>
+#include <linux/sched.h>
 #include <linux/xarray.h>
 
 #include "amd_iommu.h"
@@ -89,6 +90,118 @@ void amd_iommu_pci_seg_trans_devid_fini(struct amd_iommu_pci_seg *pci_seg)
 	mutex_destroy(&pci_seg->trans_devid_mutex);
 }
 
+/**
+ * trans_devid_do_relocate - move vIOMMU translation DTE from @old_id to @new_id
+ *
+ * Caller holds @aviommu->trans_devid_lock.  Pool xarray already records @new_id
+ * as allocated to @aviommu and @old_id as reserved.
+ *
+ * amd_iommu_set_translate_dte() cannot fail here: trans_dev_data is
+ * allocated in the same trans_devid_lock section as the xarray owner
+ * and is only cleared with trans_devid_free(). A later failure after
+ * the new DTE is programmed must clear that DTE before the pool drops
+ * @new_id.
+ */
+static int trans_devid_do_relocate(struct amd_iommu_viommu *aviommu,
+				   u16 old_id, u16 new_id)
+{
+	struct iommufd_viommu *viommu = &aviommu->core;
+	struct amd_iommu *iommu =
+		container_of(viommu->iommu_dev, struct amd_iommu, iommu);
+	int ret;
+
+	aviommu->trans_devid = new_id;
+
+	ret = amd_iommu_set_translate_dte(viommu);
+	if (ret)
+		goto err_restore_id;
+
+	amd_iommu_update_vfctrl_mmio_translate_devid(iommu, aviommu->gid, new_id);
+
+	amd_iommu_clear_translate_dte(iommu, aviommu->trans_dev_data, old_id);
+
+	return 0;
+
+err_restore_id:
+	aviommu->trans_devid = old_id;
+	return ret;
+}
+
+/**
+ * trans_devid_relocate - move an allocated id to a new slot and reserve @from_id
+ *
+ * Called when PCI probe needs a BDF that a vIOMMU already owns.  Updates the
+ * per-segment pool, then reprograms DTE and VFctrl on the owning vIOMMU.
+ *
+ * Locking: caller holds @aviommu->trans_devid_lock and
+ * pci_seg->trans_devid_mutex.  Hardware steps run with the viommu lock
+ * held and the segment mutex dropped.
+ */
+static int trans_devid_relocate(struct amd_iommu_pci_seg *pci_seg, u16 from_id,
+				struct amd_iommu_viommu *aviommu)
+{
+	void *old;
+	int new_id, ret;
+
+	if (trans_devid_xa_owner(xa_load(&pci_seg->trans_devid_xa, from_id)) !=
+	    aviommu) {
+		ret = -ENOENT;
+		goto unlock_seg;
+	}
+
+	if (aviommu->trans_devid != from_id) {
+		ret = -EINVAL;
+		goto unlock_seg;
+	}
+
+	new_id = trans_devid_find_free_locked(pci_seg);
+	if (new_id < 0) {
+		ret = new_id;
+		goto unlock_seg;
+	}
+
+	ret = trans_devid_xa_install_allocated_locked(pci_seg, new_id, aviommu);
+	if (ret)
+		goto unlock_seg;
+
+	/*
+	 * Replace ALLOCATED with RESERVED in place. install_reserved
+	 * WARNs on a non-NULL old entry; do not erase first or a failed
+	 * store would leave from_id FREE while hardware still uses it.
+	 */
+	old = xa_store(&pci_seg->trans_devid_xa, from_id,
+		       trans_devid_xa_mk_reserved(), GFP_KERNEL);
+	if (xa_is_err(old)) {
+		xa_erase(&pci_seg->trans_devid_xa, new_id);
+		ret = xa_err(old);
+		goto unlock_seg;
+	}
+	WARN_ON_ONCE(trans_devid_xa_owner(old) != aviommu);
+
+	mutex_unlock(&pci_seg->trans_devid_mutex);
+
+	ret = trans_devid_do_relocate(aviommu, from_id, new_id);
+	if (ret) {
+		mutex_lock(&pci_seg->trans_devid_mutex);
+		xa_erase(&pci_seg->trans_devid_xa, new_id);
+		old = xa_store(&pci_seg->trans_devid_xa, from_id, aviommu,
+			       GFP_KERNEL);
+		if (xa_is_err(old))
+			ret = xa_err(old);
+		else
+			WARN_ON_ONCE(!trans_devid_xa_is_reserved(old));
+		mutex_unlock(&pci_seg->trans_devid_mutex);
+	}
+
+	mutex_unlock(&aviommu->trans_devid_lock);
+	return ret;
+
+unlock_seg:
+	mutex_unlock(&pci_seg->trans_devid_mutex);
+	mutex_unlock(&aviommu->trans_devid_lock);
+	return ret;
+}
+
 /*
  * amd_iommu_trans_devid_reserve - occupy @id so it is never returned by alloc
  *
@@ -96,18 +209,49 @@ void amd_iommu_pci_seg_trans_devid_fini(struct amd_iommu_pci_seg *pci_seg)
  * It is not released from amd_iommu_release_device(); the slot stays
  * reserved for the pci_seg lifetime so replug cannot race later alloc.
  *
- * Return: 0 on success.  A second reserve of an already-reserved @id succeeds.
+ * When @id is allocated to a vIOMMU (e.g. after PCI hot-plug), the driver relocates
+ * that vIOMMU to a newly allocated translate-device-id and reserves @id for the PCI
+ * function.
+ *
+ * Return: 0 on success, %-ENOSPC if relocation cannot find a free id, or another
+ * errno from relocation.  A second reserve of an already-reserved @id succeeds.
  */
 int amd_iommu_trans_devid_reserve(struct amd_iommu_pci_seg *pci_seg, u16 id)
 {
 	void *entry;
+	struct amd_iommu_viommu *aviommu;
 	int ret = 0;
 
+retry:
 	mutex_lock(&pci_seg->trans_devid_mutex);
 	entry = xa_load(&pci_seg->trans_devid_xa, id);
 	if (trans_devid_xa_is_reserved(entry))
 		goto unlock;
 
+	aviommu = trans_devid_xa_owner(entry);
+	if (aviommu) {
+		/*
+		 * Pin aviommu with trylock while the mutex still covers
+		 * the xarray pointer. A blocking lock here would invert
+		 * the nested order (ABBA with destroy). Dropping the
+		 * mutex first would UAF if destroy frees aviommu.
+		 *
+		 * No retry bound. cond_resched() avoids a soft lockup;
+		 * progress is this owner dropping trans_devid_lock or
+		 * freeing the slot.
+		 */
+		if (!mutex_trylock(&aviommu->trans_devid_lock)) {
+			mutex_unlock(&pci_seg->trans_devid_mutex);
+			cond_resched();
+			goto retry;
+		}
+		ret = trans_devid_relocate(pci_seg, id, aviommu);
+		if (!ret)
+			pr_debug("%s: Reserved trans_devid %#x after relocation (seg %#x)\n",
+				 __func__, id, pci_seg->id);
+		return ret;
+	}
+
 	ret = trans_devid_xa_install_reserved_locked(pci_seg, id);
 unlock:
 	mutex_unlock(&pci_seg->trans_devid_mutex);
-- 
2.34.1