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vfio/pci: Fix racy bitfields and tighten struct layout

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Bitfield operations are not atomic, they use a read-modify-write
pattern, therefore we should be careful not to pack bitfields that
can be concurrently updated into the same storage unit.

This split takes a binary approach: flags that are only modified
pre/post open/close remain bitfields, flags modified from user
action, including actions that reach across to another device (ex.
reset) use dedicated storage units.

Note that the virq_disabled and bardirty flags are relocated to fill
an existing hole in the structure.

Bitfield justifications:

  has_dyn_msix: written only in vfio_pci_core_enable()
  pci_2_3: written only in vfio_pci_core_enable()
  reset_works: written only in vfio_pci_core_enable()
  extended_caps: written only in vfio_cap_len() under vfio_config_init()
  has_vga: written only in vfio_pci_core_enable()
  nointx: written only in vfio_pci_core_enable()
  needs_pm_restore: written only in vfio_pci_probe_power_state()
  disable_idle_d3: written only at .init in vfio_pci_core_init_dev()

Dedicated storage units:

  virq_disabled: written by guest INTx command writes in
                 vfio_basic_config_write() while the device is open
  bardirty: written by guest BAR writes in vfio_basic_config_write()
            while the device is open
  pm_intx_masked: written in the runtime-PM suspend path.
  pm_runtime_engaged: written by low-power feature entry/exit paths
  needs_reset: set in vfio_pci_core_disable() and cleared for devices in
               the set by vfio_pci_dev_set_try_reset()
  sriov_active: written by vfio_pci_core_sriov_configure() via sysfs
                sriov_numvfs while bound.

Fixes: 9cd0f6d5cb ("vfio/pci: Use bitfield for struct vfio_pci_core_device flags")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Alex Williamson <alex.williamson@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20260615191241.688297-4-alex.williamson@nvidia.com
Signed-off-by: Alex Williamson <alex@shazbot.org>
This commit is contained in:
Alex Williamson 2026-06-15 13:12:31 -06:00 committed by Alex Williamson
parent daedde7f02
commit e73638e55f
1 changed files with 8 additions and 5 deletions
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13
include/linux/vfio_pci_core.h
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@ -101,6 +101,9 @@ struct vfio_pci_core_device {
const struct vfio_pci_device_ops *pci_ops;
void __iomem *barmap[PCI_STD_NUM_BARS];
bool bar_mmap_supported[PCI_STD_NUM_BARS];
/* Flags modified at runtime - dedicated storage unit */
bool virq_disabled;
bool bardirty;
u8 *pci_config_map;
u8 *vconfig;
struct perm_bits *msi_perm;
@ -115,19 +118,19 @@ struct vfio_pci_core_device {
u16 msix_size;
u32 msix_offset;
u32 rbar[7];
/* Flags only modified on setup/release - bitfield ok */
bool has_dyn_msix:1;
bool pci_2_3:1;
bool virq_disabled:1;
bool reset_works:1;
bool extended_caps:1;
bool bardirty:1;
bool has_vga:1;
bool needs_reset:1;
bool nointx:1;
bool needs_pm_restore:1;
bool pm_intx_masked:1;
bool pm_runtime_engaged:1;
bool disable_idle_d3:1;
/* Flags modified at runtime - dedicated storage unit */
bool needs_reset;
bool pm_intx_masked;
bool pm_runtime_engaged;
bool sriov_active;
struct pci_saved_state *pci_saved_state;
struct pci_saved_state *pm_save;