On Wed, Mar 17, 2021 at 08:58:34AM +0800, Lu Baolu wrote:
> The pasid_lock is used to synchronize different threads from modifying a
> same pasid directory entry at the same time. It causes below lockdep splat.
>
> [ 83.296538] ========================================================
> [ 83.296538] WARNING: possible irq lock inversion dependency detected
> [ 83.296539] 5.12.0-rc3+ #25 Tainted: G W
> [ 83.296539] --------------------------------------------------------
> [ 83.296540] bash/780 just changed the state of lock:
> [ 83.296540] ffffffff82b29c98 (device_domain_lock){..-.}-{2:2}, at:
> iommu_flush_dev_iotlb.part.0+0x32/0x110
> [ 83.296547] but this lock took another, SOFTIRQ-unsafe lock in the past:
> [ 83.296547] (pasid_lock){+.+.}-{2:2}
> [ 83.296548]
>
> and interrupts could create inverse lock ordering between them.
>
> [ 83.296549] other info that might help us debug this:
> [ 83.296549] Chain exists of:
> device_domain_lock --> &iommu->lock --> pasid_lock
> [ 83.296551] Possible interrupt unsafe locking scenario:
>
> [ 83.296551] CPU0 CPU1
> [ 83.296552] ---- ----
> [ 83.296552] lock(pasid_lock);
> [ 83.296553] local_irq_disable();
> [ 83.296553] lock(device_domain_lock);
> [ 83.296554] lock(&iommu->lock);
> [ 83.296554] <Interrupt>
> [ 83.296554] lock(device_domain_lock);
> [ 83.296555]
> *** DEADLOCK ***
>
> Fix it by replacing the pasid_lock with an atomic exchange operation.
>
> Reported-and-tested-by: Dave Jiang <dave.ji...@intel.com>
> Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
> ---
> drivers/iommu/intel/pasid.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index 9fb3d3e80408..1ddcb8295f72 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -24,7 +24,6 @@
> /*
> * Intel IOMMU system wide PASID name space:
> */
> -static DEFINE_SPINLOCK(pasid_lock);
> u32 intel_pasid_max_id = PASID_MAX;
>
> int vcmd_alloc_pasid(struct intel_iommu *iommu, u32 *pasid)
> @@ -259,19 +258,18 @@ struct pasid_entry *intel_pasid_get_entry(struct device
> *dev, u32 pasid)
> dir_index = pasid >> PASID_PDE_SHIFT;
> index = pasid & PASID_PTE_MASK;
>
> - spin_lock(&pasid_lock);
> entries = get_pasid_table_from_pde(&dir[dir_index]);
> if (!entries) {
> entries = alloc_pgtable_page(info->iommu->node);
> - if (!entries) {
> - spin_unlock(&pasid_lock);
> + if (!entries)
> return NULL;
> - }
>
> - WRITE_ONCE(dir[dir_index].val,
> - (u64)virt_to_phys(entries) | PASID_PTE_PRESENT);
> + if (cmpxchg64(&dir[dir_index].val, 0ULL,
> + (u64)virt_to_phys(entries) | PASID_PTE_PRESENT)) {
> + free_pgtable_page(entries);
> + entries = get_pasid_table_from_pde(&dir[dir_index]);
This is racy, someone could have already cleared the pasid-entry again.
What you need to do here is to retry the whole path by adding a goto
to before the first get_pasid_table_from_pde() call.
Btw, what makes sure that the pasid_entry does not go away when it is
returned here?
Regards,
Joerg
