Re: [PATCH v2 11/12] iommu/vt-d: Use device_domain_lock accurately

[Baolu Lu]

On 2022/6/14 15:16, Tian, Kevin wrote:

From: Lu Baolu 
Sent: Tuesday, June 14, 2022 10:52 AM

The device_domain_lock is used to protect the device tracking list of
a domain. Remove unnecessary spin_lock/unlock()'s and move the necessary
ones around the list access.

Signed-off-by: Lu Baolu 
---
  drivers/iommu/intel/iommu.c | 68 +++--
  1 file changed, 27 insertions(+), 41 deletions(-)


[...]

+iommu_support_dev_iotlb(struct dmar_domain *domain, struct
intel_iommu *iommu,
+   u8 bus, u8 devfn)
  {
-   struct device_domain_info *info;
-
-   assert_spin_locked(&device_domain_lock);
+   struct device_domain_info *info = NULL, *tmp;
+   unsigned long flags;

if (!iommu->qi)
return NULL;

-   list_for_each_entry(info, &domain->devices, link)
-   if (info->iommu == iommu && info->bus == bus &&
-   info->devfn == devfn) {
-   if (info->ats_supported && info->dev)
-   return info;
+   spin_lock_irqsave(&device_domain_lock, flags);
+   list_for_each_entry(tmp, &domain->devices, link) {
+   if (tmp->iommu == iommu && tmp->bus == bus &&
+   tmp->devfn == devfn) {
+   if (tmp->ats_supported)
+   info = tmp;


Directly returning with unlock here is clearer than adding
another tmp variable...


Sure.




@@ -2460,15 +2450,14 @@ static int domain_add_dev_info(struct
dmar_domain *domain, struct device *dev)
if (!iommu)
return -ENODEV;

-   spin_lock_irqsave(&device_domain_lock, flags);
-   info->domain = domain;
ret = domain_attach_iommu(domain, iommu);
-   if (ret) {
-   spin_unlock_irqrestore(&device_domain_lock, flags);
+   if (ret)
return ret;
-   }
+
+   spin_lock_irqsave(&device_domain_lock, flags);
list_add(&info->link, &domain->devices);
spin_unlock_irqrestore(&device_domain_lock, flags);
+   info->domain = domain;



This is incorrect. You need fully initialize the object before adding
it to the list. Otherwise a search right after above unlock and
before assigning info->domain will get a wrong data


Fair enough. Will fix it in the next version.

Best regards,
baolu
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RE: [PATCH v2 11/12] iommu/vt-d: Use device_domain_lock accurately

[Tian, Kevin]

> From: Lu Baolu 
> Sent: Tuesday, June 14, 2022 10:52 AM
> 
> The device_domain_lock is used to protect the device tracking list of
> a domain. Remove unnecessary spin_lock/unlock()'s and move the necessary
> ones around the list access.
> 
> Signed-off-by: Lu Baolu 
> ---
>  drivers/iommu/intel/iommu.c | 68 +++--
>  1 file changed, 27 insertions(+), 41 deletions(-)
> 
[...]
> +iommu_support_dev_iotlb(struct dmar_domain *domain, struct
> intel_iommu *iommu,
> + u8 bus, u8 devfn)
>  {
> - struct device_domain_info *info;
> -
> - assert_spin_locked(&device_domain_lock);
> + struct device_domain_info *info = NULL, *tmp;
> + unsigned long flags;
> 
>   if (!iommu->qi)
>   return NULL;
> 
> - list_for_each_entry(info, &domain->devices, link)
> - if (info->iommu == iommu && info->bus == bus &&
> - info->devfn == devfn) {
> - if (info->ats_supported && info->dev)
> - return info;
> + spin_lock_irqsave(&device_domain_lock, flags);
> + list_for_each_entry(tmp, &domain->devices, link) {
> + if (tmp->iommu == iommu && tmp->bus == bus &&
> + tmp->devfn == devfn) {
> + if (tmp->ats_supported)
> + info = tmp;

Directly returning with unlock here is clearer than adding
another tmp variable...

> @@ -2460,15 +2450,14 @@ static int domain_add_dev_info(struct
> dmar_domain *domain, struct device *dev)
>   if (!iommu)
>   return -ENODEV;
> 
> - spin_lock_irqsave(&device_domain_lock, flags);
> - info->domain = domain;
>   ret = domain_attach_iommu(domain, iommu);
> - if (ret) {
> - spin_unlock_irqrestore(&device_domain_lock, flags);
> + if (ret)
>   return ret;
> - }
> +
> + spin_lock_irqsave(&device_domain_lock, flags);
>   list_add(&info->link, &domain->devices);
>   spin_unlock_irqrestore(&device_domain_lock, flags);
> + info->domain = domain;
> 

This is incorrect. You need fully initialize the object before adding
it to the list. Otherwise a search right after above unlock and
before assigning info->domain will get a wrong data
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