Messages in this thread | | | Date | Tue, 14 Jun 2022 15:15:48 +0800 | Subject | Re: [PATCH v2 01/12] iommu/vt-d: debugfs: Remove device_domain_lock usage | From | Baolu Lu <> |
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Hi Kevin,
Thanks for your reviewing.
On 2022/6/14 14:43, Tian, Kevin wrote: >> From: Lu Baolu <baolu.lu@linux.intel.com> >> Sent: Tuesday, June 14, 2022 10:51 AM >> >> The domain_translation_struct debugfs node is used to dump the DMAR >> page >> tables for the PCI devices. It potentially races with setting domains to >> devices. The existing code uses a global spinlock device_domain_lock to >> avoid the races, but this is problematical as this lock is only used to >> protect the device tracking lists of each domain. > > is it really problematic at this point? Before following patches are applied > using device_domain_lock should have similar effect as holding the group > lock.
The device_domain_lock only protects the device tracking list of the domain, it doesn't include the domain pointer stored in the dev_info structure. That's really protected by the group->mutex.
> > Here it might make more sense to just focus on removing the use of > device_domain_lock outside of iommu.c. Just that using group lock is > cleaner and more compatible to following cleanups.
Fair enough. I will update the commit message with above statement.
> and it's worth mentioning that racing with page table updates is out > of the scope of this series. Probably also add a comment in the code > to clarify this point.
Sure.
> >> >> This replaces device_domain_lock with group->mutex to protect page tables >> from setting a new domain. This also makes device_domain_lock static as >> it is now only used inside the file. > > s/the file/iommu.c/
Sure.
> >> >> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> >> --- >> drivers/iommu/intel/iommu.h | 1 - >> drivers/iommu/intel/debugfs.c | 49 +++++++++++++++++++++++++---------- >> drivers/iommu/intel/iommu.c | 2 +- >> 3 files changed, 36 insertions(+), 16 deletions(-) >> >> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h >> index a22adfbdf870..8a6d64d726c0 100644 >> --- a/drivers/iommu/intel/iommu.h >> +++ b/drivers/iommu/intel/iommu.h >> @@ -480,7 +480,6 @@ enum { >> #define VTD_FLAG_SVM_CAPABLE (1 << 2) >> >> extern int intel_iommu_sm; >> -extern spinlock_t device_domain_lock; >> >> #define sm_supported(iommu) (intel_iommu_sm && >> ecap_smts((iommu)->ecap)) >> #define pasid_supported(iommu) (sm_supported(iommu) && >> \ >> diff --git a/drivers/iommu/intel/debugfs.c b/drivers/iommu/intel/debugfs.c >> index d927ef10641b..5ebfe32265d5 100644 >> --- a/drivers/iommu/intel/debugfs.c >> +++ b/drivers/iommu/intel/debugfs.c >> @@ -342,15 +342,23 @@ static void pgtable_walk_level(struct seq_file *m, >> struct dma_pte *pde, >> } >> } >> >> -static int show_device_domain_translation(struct device *dev, void *data) >> +struct show_domain_opaque { >> + struct device *dev; >> + struct seq_file *m; >> +}; > > Sounds redundant as both bus_for_each_dev() and > iommu_group_for_each_dev() declares the same fn type which > accepts a device pointer and void *data. > >> + >> +static int __show_device_domain_translation(struct device *dev, void *data) >> { >> - struct device_domain_info *info = dev_iommu_priv_get(dev); >> - struct dmar_domain *domain = info->domain; >> - struct seq_file *m = data; >> + struct show_domain_opaque *opaque = data; >> + struct device_domain_info *info; >> + struct seq_file *m = opaque->m; >> + struct dmar_domain *domain; >> u64 path[6] = { 0 }; >> >> - if (!domain) >> + if (dev != opaque->dev) >> return 0; > > not required.
Together with above comment.
The iommu group might have other devices. I only want to dump the domain of the secific @opaque->dev. It reads a bit confusing, but it's the only helper I can use outside of drivers/iommu/iommu.c.
Or, since all devices in the iommu group share the same domain, hence only dump once?
> >> + info = dev_iommu_priv_get(dev); >> + domain = info->domain; >> >> seq_printf(m, "Device %s @0x%llx\n", dev_name(dev), >> (u64)virt_to_phys(domain->pgd)); >> @@ -359,20 +367,33 @@ static int show_device_domain_translation(struct >> device *dev, void *data) >> pgtable_walk_level(m, domain->pgd, domain->agaw + 2, 0, path); >> seq_putc(m, '\n'); >> >> - return 0; >> + return 1; >> } >> >> -static int domain_translation_struct_show(struct seq_file *m, void *unused) >> +static int show_device_domain_translation(struct device *dev, void *data) >> { >> - unsigned long flags; >> - int ret; >> + struct show_domain_opaque opaque = {dev, data}; >> + struct iommu_group *group; >> >> - spin_lock_irqsave(&device_domain_lock, flags); >> - ret = bus_for_each_dev(&pci_bus_type, NULL, m, >> - show_device_domain_translation); >> - spin_unlock_irqrestore(&device_domain_lock, flags); >> + group = iommu_group_get(dev); >> + if (group) { >> + /* >> + * The group->mutex is held across the callback, which will >> + * block calls to iommu_attach/detach_group/device. Hence, >> + * the domain of the device will not change during traversal. >> + */ >> + iommu_group_for_each_dev(group, &opaque, >> + __show_device_domain_translation); >> + iommu_group_put(group); >> + } >> >> - return ret; >> + return 0; >> +} >> + >> +static int domain_translation_struct_show(struct seq_file *m, void *unused) >> +{ >> + return bus_for_each_dev(&pci_bus_type, NULL, m, >> + show_device_domain_translation); >> } >> DEFINE_SHOW_ATTRIBUTE(domain_translation_struct); >> >> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c >> index 19024dc52735..a39d72a9d1cf 100644 >> --- a/drivers/iommu/intel/iommu.c >> +++ b/drivers/iommu/intel/iommu.c >> @@ -314,7 +314,7 @@ static int iommu_skip_te_disable; >> #define IDENTMAP_GFX 2 >> #define IDENTMAP_AZALIA 4 >> >> -DEFINE_SPINLOCK(device_domain_lock); >> +static DEFINE_SPINLOCK(device_domain_lock); >> static LIST_HEAD(device_domain_list); >> >> /* >> -- >> 2.25.1 >
Best regards, baolu
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