[PATCH 6/9] vfio/pci: Clean up BAR zap and revocation

Matt Evans
2026-04-16T13:19:01Z

Previously, vfio_pci_zap_bars() (and the wrapper
vfio_pci_zap_and_down_write_memory_lock()) calls were paired with
calls of vfio_pci_dma_buf_move().

This commit replaces them a unified new function,
vfio_pci_zap_revoke_bars() containing both the vfio_pci_dma_buf_move()
and the unmap_mapping_range(), making it harder for callers to omit
one. It adds a wrapper, vfio_pci_lock_zap_revoke_bars(), which takes
the write memory_lock before zapping, and adds a new
vfio_pci_unrevoke_bars() for the re-enable path.

However, as of "vfio/pci: Convert BAR mmap() to use a DMABUF" the
unmap_mapping_range() to zap is entirely redundant for plain vfio-pci,
since the DMABUFs used for BAR mappings already zap PTEs when the
vfio_pci_dma_buf_move() occurs.

One exception remains as a FIXME: in nvgrace-gpu, some BAR VMAs
conditionally use custom vm_ops, which have not moved to be backed by
DMABUFs. If these BARs are mmap()ed, the vdev enables the existing
behaviour of unmap_mapping_range() for the device fd address space.

Signed-off-by: Matt Evans <mattev@meta.com>
---
drivers/vfio/pci/nvgrace-gpu/main.c | 5 +++
drivers/vfio/pci/vfio_pci_config.c | 30 ++++++--------
drivers/vfio/pci/vfio_pci_core.c | 62 +++++++++++++++++++----------
drivers/vfio/pci/vfio_pci_priv.h | 3 +-
include/linux/vfio_pci_core.h | 1 +
5 files changed, 62 insertions(+), 39 deletions(-)

diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-gpu/main.c
index c1df437754f9..5304d15b9a2b 100644
--- a/drivers/vfio/pci/nvgrace-gpu/main.c
+++ b/drivers/vfio/pci/nvgrace-gpu/main.c
@@ -358,6 +358,8 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
struct nvgrace_gpu_pci_core_device *nvdev =
container_of(core_vdev, struct nvgrace_gpu_pci_core_device,
core_device.vdev);
+ struct vfio_pci_core_device *vdev =
+ container_of(core_vdev, struct vfio_pci_core_device, vdev);
struct mem_region *memregion;
u64 req_len, pgoff, end;
unsigned int index;
@@ -368,6 +370,9 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
if (!memregion)
return vfio_pci_core_mmap(core_vdev, vma);

+ /* Non-DMABUF BAR mappings need an extra zap */
+ vdev->bar_needs_zap = true;
+
/*
* Request to mmap the BAR. Map to the CPU accessible memory on the
* GPU using the memory information gathered from the system ACPI
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index a10ed733f0e3..8bfab0da481c 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -590,12 +590,10 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
virt_mem = !!(le16_to_cpu(*virt_cmd) & PCI_COMMAND_MEMORY);
new_mem = !!(new_cmd & PCI_COMMAND_MEMORY);

- if (!new_mem) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
- } else {
+ if (!new_mem)
+ vfio_pci_lock_zap_revoke_bars(vdev);
+ else
down_write(&vdev->memory_lock);
- }

/*
* If the user is writing mem/io enable (new_mem/io) and we
@@ -631,7 +629,7 @@ static int vfio_basic_config_write(struct vfio_pci_core_device *vdev, int pos,
*virt_cmd |= cpu_to_le16(new_cmd & mask);

if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}

@@ -712,16 +710,14 @@ static int __init init_pci_cap_basic_perm(struct perm_bits *perm)
static void vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
pci_power_t state)
{
- if (state >= PCI_D3hot) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
- } else {
+ if (state >= PCI_D3hot)
+ vfio_pci_lock_zap_revoke_bars(vdev);
+ else
down_write(&vdev->memory_lock);
- }

vfio_pci_set_power_state(vdev, state);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}

@@ -908,11 +904,10 @@ static int vfio_exp_config_write(struct vfio_pci_core_device *vdev, int pos,
&cap);

if (!ret && (cap & PCI_EXP_DEVCAP_FLR)) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_lock_zap_revoke_bars(vdev);
pci_try_reset_function(vdev->pdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
}
@@ -993,11 +988,10 @@ static int vfio_af_config_write(struct vfio_pci_core_device *vdev, int pos,
&cap);

if (!ret && (cap & PCI_AF_CAP_FLR) && (cap & PCI_AF_CAP_TP)) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_lock_zap_revoke_bars(vdev);
pci_try_reset_function(vdev->pdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}
}
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index c00a61d61250..464b63585bef 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -319,8 +319,7 @@ static int vfio_pci_runtime_pm_entry(struct vfio_pci_core_device *vdev,
* The vdev power related flags are protected with 'memory_lock'
* semaphore.
*/
- vfio_pci_zap_and_down_write_memory_lock(vdev);
- vfio_pci_dma_buf_move(vdev, true);
+ vfio_pci_lock_zap_revoke_bars(vdev);

if (vdev->pm_runtime_engaged) {
up_write(&vdev->memory_lock);
@@ -406,7 +405,7 @@ static void vfio_pci_runtime_pm_exit(struct vfio_pci_core_device *vdev)
down_write(&vdev->memory_lock);
__vfio_pci_runtime_pm_exit(vdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}

@@ -1229,7 +1228,7 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
if (!vdev->reset_works)
return -EINVAL;

- vfio_pci_zap_and_down_write_memory_lock(vdev);
+ vfio_pci_lock_zap_revoke_bars(vdev);

/*
* This function can be invoked while the power state is non-D0. If
@@ -1242,10 +1241,9 @@ static int vfio_pci_ioctl_reset(struct vfio_pci_core_device *vdev,
*/
vfio_pci_set_power_state(vdev, PCI_D0);

- vfio_pci_dma_buf_move(vdev, true);
ret = pci_try_reset_function(vdev->pdev);
if (__vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);

return ret;
@@ -1613,20 +1611,44 @@ ssize_t vfio_pci_core_write(struct vfio_device *core_vdev, const char __user *bu
}
EXPORT_SYMBOL_GPL(vfio_pci_core_write);

-static void vfio_pci_zap_bars(struct vfio_pci_core_device *vdev)
+static void vfio_pci_zap_revoke_bars(struct vfio_pci_core_device *vdev)
{
- struct vfio_device *core_vdev = &vdev->vdev;
- loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
- loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
- loff_t len = end - start;
+ lockdep_assert_held_write(&vdev->memory_lock);
+ vfio_pci_dma_buf_move(vdev, true);

- unmap_mapping_range(core_vdev->inode->i_mapping, start, len, true);
+ /*
+ * All VFIO PCI BARs are backed by DMABUFs, with the current
+ * exception of the nvgrace-gpu device which uses its own
+ * vm_ops for a subset of BARs. For this, BAR mappings are
+ * still made in the vdev's address_space, and a zap is
+ * required. The tracking is crude, and will (harmlessly)
+ * continue to zap if the special BAR is unmapped, but that
+ * behaviour isn't the common case.
+ *
+ * FIXME: This can go away if the special nvgrace-gpu mapping
+ * is converted to use DMABUF.
+ */
+ if (vdev->bar_needs_zap) {
+ struct vfio_device *core_vdev = &vdev->vdev;
+ loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX);
+ loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX);
+ loff_t len = end - start;
+
+ unmap_mapping_range(core_vdev->inode->i_mapping,
+ start, len, true);
+ }
}

-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev)
+void vfio_pci_lock_zap_revoke_bars(struct vfio_pci_core_device *vdev)
{
down_write(&vdev->memory_lock);
- vfio_pci_zap_bars(vdev);
+ vfio_pci_zap_revoke_bars(vdev);
+}
+
+void vfio_pci_unrevoke_bars(struct vfio_pci_core_device *vdev)
+{
+ lockdep_assert_held_write(&vdev->memory_lock);
+ vfio_pci_dma_buf_move(vdev, false);
}

u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev)
@@ -2480,9 +2502,10 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
}

/*
- * Take the memory write lock for each device and zap BAR
- * mappings to prevent the user accessing the device while in
- * reset. Locking multiple devices is prone to deadlock,
+ * Take the memory write lock for each device and
+ * zap/revoke BAR mappings to prevent the user (or
+ * peers) accessing the device while in reset.
+ * Locking multiple devices is prone to deadlock,
* runaway and unwind if we hit contention.
*/
if (!down_write_trylock(&vdev->memory_lock)) {
@@ -2490,8 +2513,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
break;
}

- vfio_pci_dma_buf_move(vdev, true);
- vfio_pci_zap_bars(vdev);
+ vfio_pci_zap_revoke_bars(vdev);
}

if (!list_entry_is_head(vdev,
@@ -2521,7 +2543,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
list_for_each_entry_from_reverse(vdev, &dev_set->device_list,
vdev.dev_set_list) {
if (vdev->vdev.open_count && __vfio_pci_memory_enabled(vdev))
- vfio_pci_dma_buf_move(vdev, false);
+ vfio_pci_unrevoke_bars(vdev);
up_write(&vdev->memory_lock);
}

diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 868a54ba482c..a8edbee6ce56 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -82,7 +82,8 @@ void vfio_config_free(struct vfio_pci_core_device *vdev);
int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev,
pci_power_t state);

-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev);
+void vfio_pci_lock_zap_revoke_bars(struct vfio_pci_core_device *vdev);
+void vfio_pci_unrevoke_bars(struct vfio_pci_core_device *vdev);
u16 vfio_pci_memory_lock_and_enable(struct vfio_pci_core_device *vdev);
void vfio_pci_memory_unlock_and_restore(struct vfio_pci_core_device *vdev,
u16 cmd);
diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 2ea4e773c121..c1cd67741125 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -127,6 +127,7 @@ struct vfio_pci_core_device {
bool needs_pm_restore:1;
bool pm_intx_masked:1;
bool pm_runtime_engaged:1;
+ bool bar_needs_zap:1;
struct pci_saved_state *pci_saved_state;
struct pci_saved_state *pm_save;
int ioeventfds_nr;
--
2.47.3