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SubjectRe: [PATCH] PCI: Fix race condition between block_cfg_access and msi_enabled/msix_enabled
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+cc linux-pci as I forgot.


On 2020/9/7 19:06, Yicong Yang wrote:
> Previously we use bit field for block_cfg_access and
> msi_enabled/msix_enabled, which is non-atomic and they may race
> each other as they share the same memory region. A race condition
> is met between driver bind vs FLR through sysfs:
>
> for driver bind side in thread 1:
> ...
> device_lock()
> ...
> ->probe()
> pci_alloc_irq_vectors_affinity()
> __pci_enable_msi_range()
> msi_capability_init()
> dev->msi_enabled=1 <---set here
> request_irq(pci_irq_vector(),...)
>
> when echo 1 > reset in thread 2:
> pci_reset_function()
> pci_dev_lock()
> pci_cfg_access_lock()
> dev->block_cfg_access=1 <---may overwrite msi_enabled bit
> device_lock()
>
> The msi_enabled bit may be overwritten to 0 and will trigger the WARN
> assert in pci_irq_vector(). A similar issue has been addressed in
> commit 44bda4b7d26e ("PCI: Fix is_added/is_busmaster race condition").
>
> Move the block_cfg_access to the pci_dev->priv_flags and use atomic
> bit operations to avoid the race condition.
>
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> ---
> drivers/pci/access.c | 20 ++++++++++----------
> drivers/pci/pci.h | 11 +++++++++++
> include/linux/pci.h | 1 -
> 3 files changed, 21 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/pci/access.c b/drivers/pci/access.c
> index 4693569..5826962 100644
> --- a/drivers/pci/access.c
> +++ b/drivers/pci/access.c
> @@ -208,9 +208,9 @@ static noinline void pci_wait_cfg(struct pci_dev *dev)
> {
> do {
> raw_spin_unlock_irq(&pci_lock);
> - wait_event(pci_cfg_wait, !dev->block_cfg_access);
> + wait_event(pci_cfg_wait, !pci_dev_is_cfg_access_blocked(dev));
> raw_spin_lock_irq(&pci_lock);
> - } while (dev->block_cfg_access);
> + } while (pci_dev_is_cfg_access_blocked(dev));
> }
>
> /* Returns 0 on success, negative values indicate error. */
> @@ -223,7 +223,7 @@ int pci_user_read_config_##size \
> if (PCI_##size##_BAD) \
> return -EINVAL; \
> raw_spin_lock_irq(&pci_lock); \
> - if (unlikely(dev->block_cfg_access)) \
> + if (unlikely(pci_dev_is_cfg_access_blocked(dev))) \
> pci_wait_cfg(dev); \
> ret = dev->bus->ops->read(dev->bus, dev->devfn, \
> pos, sizeof(type), &data); \
> @@ -242,7 +242,7 @@ int pci_user_write_config_##size \
> if (PCI_##size##_BAD) \
> return -EINVAL; \
> raw_spin_lock_irq(&pci_lock); \
> - if (unlikely(dev->block_cfg_access)) \
> + if (unlikely(pci_dev_is_cfg_access_blocked(dev))) \
> pci_wait_cfg(dev); \
> ret = dev->bus->ops->write(dev->bus, dev->devfn, \
> pos, sizeof(type), val); \
> @@ -271,9 +271,9 @@ void pci_cfg_access_lock(struct pci_dev *dev)
> might_sleep();
>
> raw_spin_lock_irq(&pci_lock);
> - if (dev->block_cfg_access)
> + if (pci_dev_is_cfg_access_blocked(dev))
> pci_wait_cfg(dev);
> - dev->block_cfg_access = 1;
> + pci_dev_block_cfg_access(dev, true);
> raw_spin_unlock_irq(&pci_lock);
> }
> EXPORT_SYMBOL_GPL(pci_cfg_access_lock);
> @@ -292,10 +292,10 @@ bool pci_cfg_access_trylock(struct pci_dev *dev)
> bool locked = true;
>
> raw_spin_lock_irqsave(&pci_lock, flags);
> - if (dev->block_cfg_access)
> + if (pci_dev_is_cfg_access_blocked(dev))
> locked = false;
> else
> - dev->block_cfg_access = 1;
> + pci_dev_block_cfg_access(dev, true);
> raw_spin_unlock_irqrestore(&pci_lock, flags);
>
> return locked;
> @@ -318,9 +318,9 @@ void pci_cfg_access_unlock(struct pci_dev *dev)
> * This indicates a problem in the caller, but we don't need
> * to kill them, unlike a double-block above.
> */
> - WARN_ON(!dev->block_cfg_access);
> + WARN_ON(!pci_dev_is_cfg_access_blocked(dev));
>
> - dev->block_cfg_access = 0;
> + pci_dev_block_cfg_access(dev, false);
> raw_spin_unlock_irqrestore(&pci_lock, flags);
>
> wake_up_all(&pci_cfg_wait);
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 73740dd..1cf3122 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -410,6 +410,7 @@ static inline bool pci_dev_is_disconnected(const struct pci_dev *dev)
>
> /* pci_dev priv_flags */
> #define PCI_DEV_ADDED 0
> +#define PCI_DEV_BLOCK_CFG_ACCESS 1 /* Config space access blocked */
>
> static inline void pci_dev_assign_added(struct pci_dev *dev, bool added)
> {
> @@ -421,6 +422,16 @@ static inline bool pci_dev_is_added(const struct pci_dev *dev)
> return test_bit(PCI_DEV_ADDED, &dev->priv_flags);
> }
>
> +static inline void pci_dev_block_cfg_access(struct pci_dev *dev, bool block)
> +{
> + assign_bit(PCI_DEV_BLOCK_CFG_ACCESS, &dev->priv_flags, block);
> +}
> +
> +static inline bool pci_dev_is_cfg_access_blocked(struct pci_dev *dev)
> +{
> + return test_bit(PCI_DEV_BLOCK_CFG_ACCESS, &dev->priv_flags);
> +}
> +
> #ifdef CONFIG_PCIEAER
> #include <linux/aer.h>
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 8355306..4ffb588 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -406,7 +406,6 @@ struct pci_dev {
> unsigned int is_busmaster:1; /* Is busmaster */
> unsigned int no_msi:1; /* May not use MSI */
> unsigned int no_64bit_msi:1; /* May only use 32-bit MSIs */
> - unsigned int block_cfg_access:1; /* Config space access blocked */
> unsigned int broken_parity_status:1; /* Generates false positive parity */
> unsigned int irq_reroute_variant:2; /* Needs IRQ rerouting variant */
> unsigned int msi_enabled:1;

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