Re: [PATCH v6 2/5] PCI: Add locking of upstream bridge for pci_reset_function()

[Alex Williamson <alex.williamson@redhat.com>]

On Thu,  2 May 2024 09:57:31 -0700
Dave Jiang <dave.jiang@intel.com> wrote:

> Fix a long standing locking gap for missing pci_cfg_access_lock() while
> manipulating bridge reset registers and configuration during
> pci_reset_bus_function(). Add calling of pci_dev_lock() against the
> bridge device before locking the device. The locking is conditional
> depending on whether the trigger device has an upstream bridge. If
> the device is a root port then there would be no upstream bridge and
> thus the locking of the bridge is unnecessary. As part of calling
> pci_dev_lock(), pci_cfg_access_lock() happens and blocks the writing
> of PCI config space by user space.
> 
> Add lockdep assertion via pci_dev->cfg_access_lock in order to verify
> pci_dev->block_cfg_access is set.
> 
> Co-developed-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/pci/access.c    |  4 ++++
>  drivers/pci/pci.c       | 13 +++++++++++++
>  drivers/pci/probe.c     |  3 +++
>  include/linux/lockdep.h |  5 +++++
>  include/linux/pci.h     |  2 ++
>  5 files changed, 27 insertions(+)
> 
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 6449056b57dd..36f10c7f9ef5 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -275,6 +275,8 @@ void pci_cfg_access_lock(struct pci_dev *dev)
>  {
>  	might_sleep();
>  
> +	lock_map_acquire(&dev->cfg_access_lock);
> +
>  	raw_spin_lock_irq(&pci_lock);
>  	if (dev->block_cfg_access)
>  		pci_wait_cfg(dev);
> @@ -329,6 +331,8 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
>  	raw_spin_unlock_irqrestore(&pci_lock, flags);
>  
>  	wake_up_all(&pci_cfg_wait);
> +
> +	lock_map_release(&dev->cfg_access_lock);


This doesn't account for config access locks acquired via
pci_cfg_access_trylock(), such as the pci_dev_trylock() through
pci_try_reset_function() resulting in a new lockdep warning for
vfio-pci when we try to release a lock that was never acquired.
Thanks,

Alex

>  }
>  EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);
>  
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e5f243dd4288..482372f5d268 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4879,6 +4879,7 @@ void __weak pcibios_reset_secondary_bus(struct pci_dev *dev)
>   */
>  int pci_bridge_secondary_bus_reset(struct pci_dev *dev)
>  {
> +	lock_map_assert_held(&dev->cfg_access_lock);
>  	pcibios_reset_secondary_bus(dev);
>  
>  	return pci_bridge_wait_for_secondary_bus(dev, "bus reset");
> @@ -5245,11 +5246,20 @@ void pci_init_reset_methods(struct pci_dev *dev)
>   */
>  int pci_reset_function(struct pci_dev *dev)
>  {
> +	struct pci_dev *bridge;
>  	int rc;
>  
>  	if (!pci_reset_supported(dev))
>  		return -ENOTTY;
>  
> +	bridge = pci_upstream_bridge(dev);
> +	/*
> +	 * If there's no upstream bridge, then no locking is needed since there is no
> +	 * upstream bridge configuration to hold consistent.
> +	 */
> +	if (bridge)
> +		pci_dev_lock(bridge);
> +
>  	pci_dev_lock(dev);
>  	pci_dev_save_and_disable(dev);
>  
> @@ -5258,6 +5268,9 @@ int pci_reset_function(struct pci_dev *dev)
>  	pci_dev_restore(dev);
>  	pci_dev_unlock(dev);
>  
> +	if (bridge)
> +		pci_dev_unlock(bridge);
> +
>  	return rc;
>  }
>  EXPORT_SYMBOL_GPL(pci_reset_function);
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 1325fbae2f28..a3da776bf986 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2543,6 +2543,9 @@ void pci_device_add(struct pci_dev *dev, struct pci_bus *bus)
>  	dev->dev.dma_mask = &dev->dma_mask;
>  	dev->dev.dma_parms = &dev->dma_parms;
>  	dev->dev.coherent_dma_mask = 0xffffffffull;
> +	lockdep_register_key(&dev->cfg_access_key);
> +	lockdep_init_map(&dev->cfg_access_lock, dev_name(&dev->dev),
> +			 &dev->cfg_access_key, 0);
>  
>  	dma_set_max_seg_size(&dev->dev, 65536);
>  	dma_set_seg_boundary(&dev->dev, 0xffffffff);
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index 08b0d1d9d78b..5e51b0de4c4b 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -297,6 +297,9 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
>  		.wait_type_inner = _wait_type,		\
>  		.lock_type = LD_LOCK_WAIT_OVERRIDE, }
>  
> +#define lock_map_assert_held(l)		\
> +	lockdep_assert(lock_is_held(l) != LOCK_STATE_NOT_HELD)
> +
>  #else /* !CONFIG_LOCKDEP */
>  
>  static inline void lockdep_init_task(struct task_struct *task)
> @@ -388,6 +391,8 @@ extern int lockdep_is_held(const void *);
>  #define DEFINE_WAIT_OVERRIDE_MAP(_name, _wait_type)	\
>  	struct lockdep_map __maybe_unused _name = {}
>  
> +#define lock_map_assert_held(l)			do { (void)(l); } while (0)
> +
>  #endif /* !LOCKDEP */
>  
>  #ifdef CONFIG_PROVE_LOCKING
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 16493426a04f..e4e7b175af54 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -413,6 +413,8 @@ struct pci_dev {
>  	struct resource driver_exclusive_resource;	 /* driver exclusive resource ranges */
>  
>  	bool		match_driver;		/* Skip attaching driver */
> +	struct lock_class_key cfg_access_key;
> +	struct lockdep_map cfg_access_lock;
>  
>  	unsigned int	transparent:1;		/* Subtractive decode bridge */
>  	unsigned int	io_window:1;		/* Bridge has I/O window */