Re: [PATCH 2/6] iommu/amd: Remove amd_iommu_devtable_lock

["Sironi, Filippo via iommu" <iommu@lists.linux-foundation.org>]

> On 25. Sep 2019, at 06:22, Joerg Roedel <joro@8bytes.org> wrote:
> 
> From: Joerg Roedel <jroedel@suse.de>
> 
> The lock is not necessary because the device table does not
> contain shared state that needs protection. Locking is only
> needed on an individual entry basis, and that needs to
> happen on the iommu_dev_data level.
> 
> Fixes: 92d420ec028d ("iommu/amd: Relax locking in dma_ops path")
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> drivers/iommu/amd_iommu.c | 23 ++++++-----------------
> 1 file changed, 6 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> index 042854bbc5bc..37a9c04fc728 100644
> --- a/drivers/iommu/amd_iommu.c
> +++ b/drivers/iommu/amd_iommu.c
> @@ -70,7 +70,6 @@
>  */
> #define AMD_IOMMU_PGSIZES	((~0xFFFUL) & ~(2ULL << 38))
> 
> -static DEFINE_SPINLOCK(amd_iommu_devtable_lock);
> static DEFINE_SPINLOCK(pd_bitmap_lock);
> 
> /* List of all available dev_data structures */
> @@ -2080,10 +2079,11 @@ static void do_detach(struct iommu_dev_data *dev_data)
> static int __attach_device(struct iommu_dev_data *dev_data,
> 			   struct protection_domain *domain)
> {
> +	unsigned long flags;
> 	int ret;
> 
> 	/* lock domain */
> -	spin_lock(&domain->lock);
> +	spin_lock_irqsave(&domain->lock, flags);
> 
> 	ret = -EBUSY;
> 	if (dev_data->domain != NULL)
> @@ -2097,7 +2097,7 @@ static int __attach_device(struct iommu_dev_data *dev_data,
> out_unlock:
> 
> 	/* ready */
> -	spin_unlock(&domain->lock);
> +	spin_unlock_irqrestore(&domain->lock, flags);
> 
> 	return ret;
> }
> @@ -2181,7 +2181,6 @@ static int attach_device(struct device *dev,
> {
> 	struct pci_dev *pdev;
> 	struct iommu_dev_data *dev_data;
> -	unsigned long flags;
> 	int ret;
> 
> 	dev_data = get_dev_data(dev);
> @@ -2209,9 +2208,7 @@ static int attach_device(struct device *dev,
> 	}
> 
> skip_ats_check:
> -	spin_lock_irqsave(&amd_iommu_devtable_lock, flags);
> 	ret = __attach_device(dev_data, domain);
> -	spin_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
> 
> 	/*
> 	 * We might boot into a crash-kernel here. The crashed kernel
> @@ -2231,14 +2228,15 @@ static int attach_device(struct device *dev,
> static void __detach_device(struct iommu_dev_data *dev_data)
> {
> 	struct protection_domain *domain;
> +	unsigned long flags;
> 
> 	domain = dev_data->domain;
> 
> -	spin_lock(&domain->lock);
> +	spin_lock_irqsave(&domain->lock, flags);
> 
> 	do_detach(dev_data);
> 
> -	spin_unlock(&domain->lock);
> +	spin_unlock_irqrestore(&domain->lock, flags);
> }
> 
> /*
> @@ -2248,7 +2246,6 @@ static void detach_device(struct device *dev)
> {
> 	struct protection_domain *domain;
> 	struct iommu_dev_data *dev_data;
> -	unsigned long flags;
> 
> 	dev_data = get_dev_data(dev);
> 	domain   = dev_data->domain;
> @@ -2262,10 +2259,7 @@ static void detach_device(struct device *dev)
> 	if (WARN_ON(!dev_data->domain))
> 		return;
> 
> -	/* lock device table */
> -	spin_lock_irqsave(&amd_iommu_devtable_lock, flags);
> 	__detach_device(dev_data);
> -	spin_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
> 
> 	if (!dev_is_pci(dev))
> 		return;
> @@ -2910,9 +2904,6 @@ int __init amd_iommu_init_dma_ops(void)
> static void cleanup_domain(struct protection_domain *domain)
> {
> 	struct iommu_dev_data *entry;
> -	unsigned long flags;
> -
> -	spin_lock_irqsave(&amd_iommu_devtable_lock, flags);
> 
> 	while (!list_empty(&domain->dev_list)) {
> 		entry = list_first_entry(&domain->dev_list,
> @@ -2920,8 +2911,6 @@ static void cleanup_domain(struct protection_domain *domain)
> 		BUG_ON(!entry->domain);
> 		__detach_device(entry);
> 	}
> -
> -	spin_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
> }

I'm guessing that it is free not to take the domain lock in cleanup_domain
since this is called when free-ing the domain.  Right?

> static void protection_domain_free(struct protection_domain *domain)
> -- 
> 2.17.1
> 




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