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Message-ID: <1161fe02-7dbb-6f97-39c0-a84be016e0a9@linux.intel.com>
Date: Tue, 14 Jun 2022 15:15:48 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>,
Joerg Roedel <joro@...tes.org>,
"Raj, Ashok" <ashok.raj@...el.com>,
Christoph Hellwig <hch@...radead.org>,
Jason Gunthorpe <jgg@...dia.com>
Cc: baolu.lu@...ux.intel.com, Will Deacon <will@...nel.org>,
Robin Murphy <robin.murphy@....com>,
"Liu, Yi L" <yi.l.liu@...el.com>,
"Pan, Jacob jun" <jacob.jun.pan@...el.com>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/12] iommu/vt-d: debugfs: Remove device_domain_lock
usage
Hi Kevin,
Thanks for your reviewing.
On 2022/6/14 14:43, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.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@...ux.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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