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From: Jerry Snitselaar <jsnitsel@redhat.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: Filippo Sironi <sironi@amazon.de>,
	iommu@lists.linux-foundation.org, jroedel@suse.de
Subject: Re: [PATCH 2/6] iommu/amd: Remove amd_iommu_devtable_lock
Date: Wed, 25 Sep 2019 23:24:52 -0700
Message-ID: <20190926062451.olmmbpjkdnwljzd7@cantor> (raw)
In-Reply-To: <20190925132300.3038-3-joro@8bytes.org>

On Wed Sep 25 19, Joerg Roedel 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);
> }
>
> static void protection_domain_free(struct protection_domain *domain)
>-- 
>2.17.1
>
>_______________________________________________
>iommu mailing list
>iommu@lists.linux-foundation.org
>https://lists.linuxfoundation.org/mailman/listinfo/iommu

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

  parent reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-25 13:22 [PATCH 0/6] iommu/amd: Locking Fixes Joerg Roedel
2019-09-25 13:22 ` [PATCH 1/6] iommu/amd: Remove domain->updated Joerg Roedel
2019-09-25 15:45   ` Sironi, Filippo via iommu
2019-09-26  6:18   ` Jerry Snitselaar
2019-09-25 13:22 ` [PATCH 2/6] iommu/amd: Remove amd_iommu_devtable_lock Joerg Roedel
2019-09-25 15:50   ` Sironi, Filippo via iommu
2019-09-25 15:52     ` Sironi, Filippo via iommu
2019-09-26  6:24   ` Jerry Snitselaar [this message]
2019-09-25 13:22 ` [PATCH 3/6] iommu/amd: Take domain->lock for complete attach/detach path Joerg Roedel
2019-09-25 15:53   ` Sironi, Filippo via iommu
2019-09-26  6:34   ` Jerry Snitselaar
2019-09-25 13:22 ` [PATCH 4/6] iommu/amd: Check for busy devices earlier in attach_device() Joerg Roedel
2019-09-25 15:55   ` Sironi, Filippo via iommu
2019-09-26  6:37   ` Jerry Snitselaar
2019-09-25 13:22 ` [PATCH 5/6] iommu/amd: Lock dev_data in attach/detach code paths Joerg Roedel
2019-09-25 15:56   ` Sironi, Filippo via iommu
2019-09-26  6:41   ` Jerry Snitselaar
2019-09-25 13:23 ` [PATCH 6/6] iommu/amd: Lock code paths traversing protection_domain->dev_list Joerg Roedel
2019-09-25 15:58   ` Sironi, Filippo via iommu
2019-09-26  6:48   ` Jerry Snitselaar
2019-09-26  0:25 ` [PATCH 0/6] iommu/amd: Locking Fixes Jerry Snitselaar
2019-09-26  5:46   ` Joerg Roedel

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