On Thu, 23 May 2024 14:17:58 -0700
Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> Alex Williamson wrote:
> > On Thu, 2 May 2024 09:57:31 -0700
> > Dave Jiang <dave.jiang@xxxxxxxxx> 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@xxxxxxxxx>
> > > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > > Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> > > ---
> [..]
> > > 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,
>
> Hey Alex, sorry about that, does this fix it up for you? Note I move the
> lock_map_acquire() relative to the global pci_lock just for symmetry
> purposes.
Thanks, Dan! Yes, this fixes it. Please feel free to add
Reported/Tested-by tags when you post it. Thanks!
Alex
> -- >8 --
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 30f031de9cfe..3595130ff719 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -289,11 +289,10 @@ 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);
> + lock_map_acquire(&dev->cfg_access_lock);
> dev->block_cfg_access = 1;
> raw_spin_unlock_irq(&pci_lock);
> }
> @@ -315,8 +314,10 @@ bool pci_cfg_access_trylock(struct pci_dev *dev)
> raw_spin_lock_irqsave(&pci_lock, flags);
> if (dev->block_cfg_access)
> locked = false;
> - else
> + else {
> + lock_map_acquire(&dev->cfg_access_lock);
> dev->block_cfg_access = 1;
> + }
> raw_spin_unlock_irqrestore(&pci_lock, flags);
>
> return locked;
> @@ -342,11 +343,10 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
> WARN_ON(!dev->block_cfg_access);
>
> dev->block_cfg_access = 0;
> + lock_map_release(&dev->cfg_access_lock);
> raw_spin_unlock_irqrestore(&pci_lock, flags);
>
> wake_up_all(&pci_cfg_wait);
> -
> - lock_map_release(&dev->cfg_access_lock);
> }
> EXPORT_SYMBOL_GPL(pci_cfg_access_unlock);
>
>
