Tested-and-reviewed-by: Yijing Wang <wangyijing@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
> ---
> 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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