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 <baolu.lu@xxxxxxxxxxxxxxx>
> > 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 <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   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