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vfio/pci: Expose latched module parameter policy in debugfs

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The nointxmask and disable_idle_d3 module parameters remain writable,
but vfio-pci now latches their values into each device at init.  Once a
device is registered, changing the module parameter only affects future
devices, leaving no direct way to confirm the effective policy for an
existing device.

Add a pci debugfs directory under the VFIO device debugfs root and
report the per-device nointxmask and disable_idle_d3 values.  These are
read-only debugfs views and use the same Y/N bool output convention as
the module parameters.

Read-only vfio-pci parameters, such as disable_vga, are not exposed here
because they cannot drift from the latched device value, therefore the
existing module parameter exposure via sysfs is sufficient.

Note that while only vfio-pci currently provides these options, the
implementation is in vfio-pci-core and therefore properly reflects the
device policy in the core, regardless of driver.

Assisted-by: OpenAI Codex:gpt-5
Cc: Guixin Liu <kanie@linux.alibaba.com>
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20260615191241.688297-7-alex.williamson@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
This commit is contained in:
Alex Williamson 2026-06-15 13:12:34 -06:00 committed by Alex Williamson
parent dc7fe87de4
commit 586a989d8b
2 changed files with 85 additions and 0 deletions
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26
Documentation/ABI/testing/debugfs-vfio
View File

@ -29,3 +29,29 @@ Date: Oct 2025
KernelVersion: 6.18
Contact: Cédric Le Goater <clg@redhat.com>
Description: Read the migration features of the vfio device.
What: /sys/kernel/debug/vfio/<device>/pci
Date: June 2026
KernelVersion: 7.2
Contact: Alex Williamson <alex.williamson@nvidia.com>
Description: This debugfs file directory is used for debugging
VFIO PCI devices.
What: /sys/kernel/debug/vfio/<device>/pci/nointxmask
Date: June 2026
KernelVersion: 7.2
Contact: Alex Williamson <alex.williamson@nvidia.com>
Description: Read the nointxmask policy latched for this device. This
policy governs whether the device may use PCI 2.3 style
INTx masking when supported, reporting a value of "N", or
requires APIC level INTx masking, reporting a value of "Y".
What: /sys/kernel/debug/vfio/<device>/pci/disable_idle_d3
Date: June 2026
KernelVersion: 7.2
Contact: Alex Williamson <alex.williamson@nvidia.com>
Description: Read the disable_idle_d3 policy latched for this device. This
policy governs whether the device PM runtime usage count is
kept elevated while the device is bound to the driver and
unused, reporting a value of "Y", or decremented to allow the
device to enter a low power state, reporting a value of "N".

59
drivers/vfio/pci/vfio_pci_core.c
View File

@ -11,6 +11,7 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/aperture.h>
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/eventfd.h>
#include <linux/file.h>
@ -29,6 +30,7 @@
#include <linux/sched/mm.h>
#include <linux/iommufd.h>
#include <linux/pci-p2pdma.h>
#include <linux/seq_file.h>
#if IS_ENABLED(CONFIG_EEH)
#include <asm/eeh.h>
#endif
@ -97,6 +99,60 @@ static inline bool vfio_vga_disabled(struct vfio_pci_core_device *vdev)
#endif
}
#ifdef CONFIG_VFIO_DEBUGFS
static struct vfio_pci_core_device *
vfio_pci_core_debugfs_private(struct seq_file *seq)
{
struct device *dev = seq->private;
struct vfio_device *core_vdev = container_of(dev, struct vfio_device,
device);
return container_of(core_vdev, struct vfio_pci_core_device, vdev);
}
static int vfio_pci_core_debugfs_nointxmask(struct seq_file *seq, void *data)
{
struct vfio_pci_core_device *vdev = vfio_pci_core_debugfs_private(seq);
seq_puts(seq, vdev->nointxmask ? "Y\n" : "N\n");
return 0;
}
static int vfio_pci_core_debugfs_disable_idle_d3(struct seq_file *seq,
void *data)
{
struct vfio_pci_core_device *vdev = vfio_pci_core_debugfs_private(seq);
seq_puts(seq, vdev->disable_idle_d3 ? "Y\n" : "N\n");
return 0;
}
/*
* disable_idle_d3 and nointxmask are writable module parameters latched
* per device at init, so a device's effective value can differ from the
* current parameter setting. Expose the per-device (read-only) values
* here for visibility; read-only parameters can't drift and are omitted.
*/
static void vfio_pci_core_debugfs_init(struct vfio_pci_core_device *vdev)
{
struct device *dev = &vdev->vdev.device;
struct dentry *pci_dir;
if (IS_ERR_OR_NULL(vdev->vdev.debug_root))
return;
pci_dir = debugfs_create_dir("pci", vdev->vdev.debug_root);
debugfs_create_devm_seqfile(dev, "nointxmask", pci_dir,
vfio_pci_core_debugfs_nointxmask);
debugfs_create_devm_seqfile(dev, "disable_idle_d3", pci_dir,
vfio_pci_core_debugfs_disable_idle_d3);
}
#else
static inline void vfio_pci_core_debugfs_init(struct vfio_pci_core_device *vdev)
{
}
#endif /* CONFIG_VFIO_DEBUGFS */
/*
* Our VGA arbiter participation is limited since we don't know anything
* about the device itself. However, if the device is the only VGA device
@ -2242,6 +2298,9 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev)
ret = vfio_register_group_dev(&vdev->vdev);
if (ret)
goto out_power;
vfio_pci_core_debugfs_init(vdev);
return 0;
out_power: