linux-kernel - Re: [Patch Part1 V2 01/17] iommu/vt-d: use dedicated bitmap to track remapping entry allocation status

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Date:	Mon, 2 Dec 2013 09:38:26 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Joerg Roedel <joro@...tes.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"Dan Williams" <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Ashok Raj <ashok.raj@...el.com>
CC:	<iommu@...ts.linux-foundation.org>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <dmaengine@...r.kernel.org>
Subject: Re: [Patch Part1 V2 01/17] iommu/vt-d: use dedicated bitmap to track
 remapping entry allocation status

Tested-and-reviewed-by: Yijing Wang <wangyijing@...wei.com>

On 2013/11/29 16:50, Jiang Liu wrote:
> Currently Intel interrupt remapping drivers uses the "present" flag bit
> in remapping entry to track whether an entry is allocated or not.
> It works as follow:
> 1) allocate a remapping entry and set its "present" flag bit to 1
> 2) compose other fields for the entry
> 3) update the remapping entry with the composed value
> 
> The remapping hardware may access the entry between step 1 and step 3,
> which then obervers an entry with the "present" flag set but random
> values in all other fields.
> 
> This patch introduces a dedicated bitmap to track remapping entry
> allocation status instead of sharing the "present" flag with hardware,
> thus eliminate the race window. It also simplifies the implementation.
> 
> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
> ---
>  drivers/iommu/intel_irq_remapping.c |   51 +++++++++++++++++------------------
>  include/linux/intel-iommu.h         |    1 +
>  2 files changed, 25 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
> index bab10b1..282d392 100644
> --- a/drivers/iommu/intel_irq_remapping.c
> +++ b/drivers/iommu/intel_irq_remapping.c
> @@ -72,7 +72,6 @@ static int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
>  	u16 index, start_index;
>  	unsigned int mask = 0;
>  	unsigned long flags;
> -	int i;
>  
>  	if (!count || !irq_iommu)
>  		return -1;
> @@ -96,32 +95,17 @@ static int alloc_irte(struct intel_iommu *iommu, int irq, u16 count)
>  	}
>  
>  	raw_spin_lock_irqsave(&irq_2_ir_lock, flags);
> -	do {
> -		for (i = index; i < index + count; i++)
> -			if  (table->base[i].present)
> -				break;
> -		/* empty index found */
> -		if (i == index + count)
> -			break;
> -
> -		index = (index + count) % INTR_REMAP_TABLE_ENTRIES;
> -
> -		if (index == start_index) {
> -			raw_spin_unlock_irqrestore(&irq_2_ir_lock, flags);
> -			printk(KERN_ERR "can't allocate an IRTE\n");
> -			return -1;
> -		}
> -	} while (1);
> -
> -	for (i = index; i < index + count; i++)
> -		table->base[i].present = 1;
> -
> -	cfg->remapped = 1;
> -	irq_iommu->iommu = iommu;
> -	irq_iommu->irte_index =  index;
> -	irq_iommu->sub_handle = 0;
> -	irq_iommu->irte_mask = mask;
> -
> +	index = bitmap_find_free_region(table->bitmap,
> +					INTR_REMAP_TABLE_ENTRIES, mask);
> +	if (index < 0) {
> +		printk(KERN_ERR "can't allocate an IRTE\n");
> +	} else {
> +		cfg->remapped = 1;
> +		irq_iommu->iommu = iommu;
> +		irq_iommu->irte_index =  index;
> +		irq_iommu->sub_handle = 0;
> +		irq_iommu->irte_mask = mask;
> +	}
>  	raw_spin_unlock_irqrestore(&irq_2_ir_lock, flags);
>  
>  	return index;
> @@ -254,6 +238,8 @@ static int clear_entries(struct irq_2_iommu *irq_iommu)
>  		set_64bit(&entry->low, 0);
>  		set_64bit(&entry->high, 0);
>  	}
> +	bitmap_release_region(iommu->ir_table->bitmap, index,
> +			      irq_iommu->irte_mask);
>  
>  	return qi_flush_iec(iommu, index, irq_iommu->irte_mask);
>  }
> @@ -453,6 +439,7 @@ static int intel_setup_irq_remapping(struct intel_iommu *iommu, int mode)
>  {
>  	struct ir_table *ir_table;
>  	struct page *pages;
> +	unsigned long *bitmap;
>  
>  	ir_table = iommu->ir_table = kzalloc(sizeof(struct ir_table),
>  					     GFP_ATOMIC);
> @@ -470,7 +457,17 @@ static int intel_setup_irq_remapping(struct intel_iommu *iommu, int mode)
>  		return -ENOMEM;
>  	}
>  
> +	bitmap = kcalloc(BITS_TO_LONGS(INTR_REMAP_TABLE_ENTRIES),
> +			 sizeof(long), GFP_ATOMIC);
> +	if (bitmap == NULL) {
> +		printk(KERN_ERR "failed to allocate bitmap\n");
> +		__free_pages(pages, INTR_REMAP_PAGE_ORDER);
> +		kfree(ir_table);
> +		return -ENOMEM;
> +	}
> +
>  	ir_table->base = page_address(pages);
> +	ir_table->bitmap = bitmap;
>  
>  	iommu_set_irq_remapping(iommu, mode);
>  	return 0;
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index d380c5e..de1e5e9 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -288,6 +288,7 @@ struct q_inval {
>  
>  struct ir_table {
>  	struct irte *base;
> +	unsigned long *bitmap;
>  };
>  #endif
>  
> 


-- 
Thanks!
Yijing

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