Re: [PATCH] iommu/amd: flush IOTLB for specific domains only (v2)

[Jan Vesely <jan.vesely-kgbqMDwikbSVc3sceRu5cw@public.gmane.org>]

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On Fri, 2017-05-19 at 15:32 +0530, arindam.nath-5C7GfCeVMHo@public.gmane.org wrote:
> From: Arindam Nath <arindam.nath-5C7GfCeVMHo@public.gmane.org>
> 
> Change History
> --------------
> 
> v2: changes suggested by Joerg
> - add flush flag to improve efficiency of flush operation
> 
> v1:
> - The idea behind flush queues is to defer the IOTLB flushing
>   for domains for which the mappings are no longer valid. We
>   add such domains in queue_add(), and when the queue size
>   reaches FLUSH_QUEUE_SIZE, we perform __queue_flush().
> 
>   Since we have already taken lock before __queue_flush()
>   is called, we need to make sure the IOTLB flushing is
>   performed as quickly as possible.
> 
>   In the current implementation, we perform IOTLB flushing
>   for all domains irrespective of which ones were actually
>   added in the flush queue initially. This can be quite
>   expensive especially for domains for which unmapping is
>   not required at this point of time.
> 
>   This patch makes use of domain information in
>   'struct flush_queue_entry' to make sure we only flush
>   IOTLBs for domains who need it, skipping others.

Hi,

just a note, the patch also fixes "AMD-Vi: Completion-Wait loop timed
out" boot hang on my system (carrizo + iceland) [0,1,2]. Presumably the
old loop also tried to flush domains that included powered-off devices.

regards,
Jan

[0] https://github.com/RadeonOpenCompute/ROCK-Kernel-Driver/issues/20
[1] https://bugs.freedesktop.org/show_bug.cgi?id=101029
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1448121

> 
> Suggested-by: Joerg Roedel <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org>
> Signed-off-by: Arindam Nath <arindam.nath-5C7GfCeVMHo@public.gmane.org>
> ---
>  drivers/iommu/amd_iommu.c       | 27 ++++++++++++++++++++-------
>  drivers/iommu/amd_iommu_types.h |  2 ++
>  2 files changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> index 63cacf5..1edeebec 100644
> --- a/drivers/iommu/amd_iommu.c
> +++ b/drivers/iommu/amd_iommu.c
> @@ -2227,15 +2227,26 @@ static struct iommu_group *amd_iommu_device_group(struct device *dev)
>  
>  static void __queue_flush(struct flush_queue *queue)
>  {
> -	struct protection_domain *domain;
> -	unsigned long flags;
>  	int idx;
>  
> -	/* First flush TLB of all known domains */
> -	spin_lock_irqsave(&amd_iommu_pd_lock, flags);
> -	list_for_each_entry(domain, &amd_iommu_pd_list, list)
> -		domain_flush_tlb(domain);
> -	spin_unlock_irqrestore(&amd_iommu_pd_lock, flags);
> +	/* First flush TLB of all domains which were added to flush queue */
> +	for (idx = 0; idx < queue->next; ++idx) {
> +		struct flush_queue_entry *entry;
> +
> +		entry = queue->entries + idx;
> +
> +		/*
> +		 * There might be cases where multiple IOVA entries for the
> +		 * same domain are queued in the flush queue. To avoid
> +		 * flushing the same domain again, we check whether the
> +		 * flag is set or not. This improves the efficiency of
> +		 * flush operation.
> +		 */
> +		if (!entry->dma_dom->domain.already_flushed) {
> +			entry->dma_dom->domain.already_flushed = true;
> +			domain_flush_tlb(&entry->dma_dom->domain);
> +		}
> +	}
>  
>  	/* Wait until flushes have completed */
>  	domain_flush_complete(NULL);
> @@ -2289,6 +2300,8 @@ static void queue_add(struct dma_ops_domain *dma_dom,
>  	pages     = __roundup_pow_of_two(pages);
>  	address >>= PAGE_SHIFT;
>  
> +	dma_dom->domain.already_flushed = false;
> +
>  	queue = get_cpu_ptr(&flush_queue);
>  	spin_lock_irqsave(&queue->lock, flags);
>  
> diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
> index 4de8f41..4f5519d 100644
> --- a/drivers/iommu/amd_iommu_types.h
> +++ b/drivers/iommu/amd_iommu_types.h
> @@ -454,6 +454,8 @@ struct protection_domain {
>  	bool updated;		/* complete domain flush required */
>  	unsigned dev_cnt;	/* devices assigned to this domain */
>  	unsigned dev_iommu[MAX_IOMMUS]; /* per-IOMMU reference count */
> +	bool already_flushed;	/* flag to avoid flushing the same domain again
> +				   in a single invocation of __queue_flush() */
>  };
>  
>  /*

-- 
Jan Vesely <jan.vesely-kgbqMDwikbSVc3sceRu5cw@public.gmane.org>

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