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