Messages in this thread | | | Date | Wed, 31 Aug 2022 11:05:48 +0200 | Subject | Re: [PATCH v3] iommu/s390: Fix race with release_device ops | From | Pierre Morel <> |
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On 8/30/22 22:15, Matthew Rosato wrote: > With commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev > calls") s390-iommu is supposed to handle dynamic switching between IOMMU > domains and the DMA API handling. However, this commit does not > sufficiently handle the case where the device is released via a call > to the release_device op as it may occur at the same time as an opposing > attach_dev or detach_dev since the group mutex is not held over > release_device. This was observed if the device is deconfigured during a > small window during vfio-pci initialization and can result in WARNs and > potential kernel panics. > > Handle this by tracking when the device is probed/released via > dev_iommu_priv_set/get(). Ensure that once the device is released only > release_device handles the re-init of the device DMA. > > Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls") > Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com> > --- > Changes since v2: > - Relocate the list_empty and aperture chekcs in attach_dev to the > their original locations so they are all done under a single > acquisition of the spinlock (Heiko) > --- > arch/s390/include/asm/pci.h | 1 + > arch/s390/pci/pci.c | 1 + > drivers/iommu/s390-iommu.c | 39 ++++++++++++++++++++++++++++++++++--- > 3 files changed, 38 insertions(+), 3 deletions(-) > > diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h > index 7b4cdadbc023..080251e7b275 100644 > --- a/arch/s390/include/asm/pci.h > +++ b/arch/s390/include/asm/pci.h > @@ -157,6 +157,7 @@ struct zpci_dev { > /* DMA stuff */ > unsigned long *dma_table; > spinlock_t dma_table_lock; > + struct mutex dma_domain_lock; /* protects s390_domain value */ > int tlb_refresh; > > spinlock_t iommu_bitmap_lock; > diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c > index 73cdc5539384..973edd32ecc9 100644 > --- a/arch/s390/pci/pci.c > +++ b/arch/s390/pci/pci.c > @@ -832,6 +832,7 @@ struct zpci_dev *zpci_create_device(u32 fid, u32 fh, enum zpci_state state) > kref_init(&zdev->kref); > mutex_init(&zdev->lock); > mutex_init(&zdev->kzdev_lock); > + mutex_init(&zdev->dma_domain_lock); > > rc = zpci_init_iommu(zdev); > if (rc) > diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c > index c898bcbbce11..1137d669e849 100644 > --- a/drivers/iommu/s390-iommu.c > +++ b/drivers/iommu/s390-iommu.c > @@ -99,6 +99,14 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, > if (!domain_device) > return -ENOMEM; > > + /* Leave now if the device has already been released */ > + mutex_lock(&zdev->dma_domain_lock); > + if (!dev_iommu_priv_get(dev)) { > + mutex_unlock(&zdev->dma_domain_lock); > + kfree(domain_device); > + return 0; > + } > + > if (zdev->dma_table && !zdev->s390_domain) { > cc = zpci_dma_exit_device(zdev); > if (cc) { > @@ -132,9 +140,10 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, > goto out_restore; > } > domain_device->zdev = zdev; > - zdev->s390_domain = s390_domain; > list_add(&domain_device->list, &s390_domain->devices); > spin_unlock_irqrestore(&s390_domain->list_lock, flags); > + zdev->s390_domain = s390_domain; > + mutex_unlock(&zdev->dma_domain_lock); > > return 0; > > @@ -147,6 +156,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain, > virt_to_phys(zdev->dma_table)); > } > out_free: > + mutex_unlock(&zdev->dma_domain_lock); > kfree(domain_device); > > return rc; > @@ -176,17 +186,22 @@ static void s390_iommu_detach_device(struct iommu_domain *domain, > } > spin_unlock_irqrestore(&s390_domain->list_lock, flags); > > - if (found && (zdev->s390_domain == s390_domain)) { > + mutex_lock(&zdev->dma_domain_lock); > + if (found && (zdev->s390_domain == s390_domain) && > + dev_iommu_priv_get(dev)) { > zdev->s390_domain = NULL; > zpci_unregister_ioat(zdev, 0); > zpci_dma_init_device(zdev); > } > + mutex_unlock(&zdev->dma_domain_lock); > } > > static struct iommu_device *s390_iommu_probe_device(struct device *dev) > { > struct zpci_dev *zdev = to_zpci_dev(dev); > > + dev_iommu_priv_set(dev, zdev); > + > return &zdev->iommu_dev; > } > > @@ -206,10 +221,28 @@ static void s390_iommu_release_device(struct device *dev) > * > * So let's call detach_dev from here if it hasn't been called before. > */ > - if (zdev && zdev->s390_domain) { > + if (zdev) { > + /* > + * Clear priv to block further attaches for this device, > + * ensure detaches don't init DMA. Hold the domain lock > + * to ensure that attach/detach get a consistent view of > + * whether or not the device is released. > + */ > + mutex_lock(&zdev->dma_domain_lock); > + dev_iommu_priv_set(dev, NULL); > + mutex_unlock(&zdev->dma_domain_lock); > + /* Make sure this device is removed from the domain list */ > domain = iommu_get_domain_for_dev(dev);
Shouldn't you take the group_mutex before calling directly s390_iommu_detach_device from here?
> if (domain) > s390_iommu_detach_device(domain, dev);
> + /* Now ensure DMA is initialized from here */ > + mutex_lock(&zdev->dma_domain_lock); > + if (zdev->s390_domain) { > + zdev->s390_domain = NULL; > + zpci_unregister_ioat(zdev, 0); > + zpci_dma_init_device(zdev); > + } > + mutex_unlock(&zdev->dma_domain_lock); > } > } > >
-- Pierre Morel IBM Lab Boeblingen
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