linux-kernel - RE: [PATCH 05/12] iommu/vt-d: Unncessary spinlock for root table alloc and free

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Date:   Wed, 1 Jun 2022 09:05:57 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Jason Gunthorpe" <jgg@...dia.com>
CC:     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 05/12] iommu/vt-d: Unncessary spinlock for root table
 alloc and free

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Friday, May 27, 2022 2:30 PM
> 
> The IOMMU root table is allocated and freed in the IOMMU initialization
> code in static boot or hot-plug paths. There's no need for a spinlock.

s/hot-plug/hot-remove/

> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>

Reviewed-by: Kevin Tian <kevin.tian@...el.com>

> ---
>  drivers/iommu/intel/iommu.c | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index bbdd3417a1b1..2d5f02b85de8 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -809,14 +809,12 @@ static int device_context_mapped(struct
> intel_iommu *iommu, u8 bus, u8 devfn)
> 
>  static void free_context_table(struct intel_iommu *iommu)
>  {
> -	int i;
> -	unsigned long flags;
>  	struct context_entry *context;
> +	int i;
> +
> +	if (!iommu->root_entry)
> +		return;
> 
> -	spin_lock_irqsave(&iommu->lock, flags);
> -	if (!iommu->root_entry) {
> -		goto out;
> -	}
>  	for (i = 0; i < ROOT_ENTRY_NR; i++) {
>  		context = iommu_context_addr(iommu, i, 0, 0);
>  		if (context)
> @@ -828,12 +826,10 @@ static void free_context_table(struct intel_iommu
> *iommu)
>  		context = iommu_context_addr(iommu, i, 0x80, 0);
>  		if (context)
>  			free_pgtable_page(context);
> -
>  	}
> +
>  	free_pgtable_page(iommu->root_entry);
>  	iommu->root_entry = NULL;
> -out:
> -	spin_unlock_irqrestore(&iommu->lock, flags);
>  }
> 
>  #ifdef CONFIG_DMAR_DEBUG
> @@ -1232,7 +1228,6 @@ static void domain_unmap(struct dmar_domain
> *domain, unsigned long start_pfn,
>  static int iommu_alloc_root_entry(struct intel_iommu *iommu)
>  {
>  	struct root_entry *root;
> -	unsigned long flags;
> 
>  	root = (struct root_entry *)alloc_pgtable_page(iommu->node);
>  	if (!root) {
> @@ -1242,10 +1237,7 @@ static int iommu_alloc_root_entry(struct
> intel_iommu *iommu)
>  	}
> 
>  	__iommu_flush_cache(iommu, root, ROOT_SIZE);
> -
> -	spin_lock_irqsave(&iommu->lock, flags);
>  	iommu->root_entry = root;
> -	spin_unlock_irqrestore(&iommu->lock, flags);
> 
>  	return 0;
>  }
> --
> 2.25.1