linux-kernel - Re: [PATCH v3 3/7] iommu/mediatek: Use gather to achieve the tlb range flush

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Message-ID: <f35c8a3a-0693-facf-2050-65d3f7628929@arm.com>
Date:   Mon, 14 Oct 2019 15:21:13 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>
Cc:     Evan Green <evgreen@...omium.org>, Tomasz Figa <tfiga@...gle.com>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>, anan.sun@...iatek.com,
        cui.zhang@...iatek.com, chao.hao@...iatek.com,
        edison.hsieh@...iatek.com
Subject: Re: [PATCH v3 3/7] iommu/mediatek: Use gather to achieve the tlb
 range flush

On 14/10/2019 07:38, Yong Wu wrote:
> Use the iommu_gather mechanism to achieve the tlb range flush.
> Gather the iova range in the "tlb_add_page", then flush the merged iova
> range in iotlb_sync.
> 
> Note: If iotlb_sync comes from iommu_iotlb_gather_add_page, we have to
> avoid retry the lock since the spinlock have already been acquired.

I think this could probably be even simpler - once the actual 
register-poking is all confined to mtk_iommu_tlb_sync(), you should be 
able get rid of the per-domain locking in map/unmap and just have a 
single per-IOMMU lock to serialise syncs. The io-pgtable code itself 
hasn't needed external locking for a while now.

Robin.

> Suggested-by: Tomasz Figa <tfiga@...omium.org>
> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
> 1) This is the special case backtrace:
> 
>   mtk_iommu_iotlb_sync+0x50/0xa0
>   mtk_iommu_tlb_flush_page_nosync+0x5c/0xd0
>   __arm_v7s_unmap+0x174/0x598
>   arm_v7s_unmap+0x30/0x48
>   mtk_iommu_unmap+0x50/0x78
>   __iommu_unmap+0xa4/0xf8
> 
> 2) The checking "if (gather->start == ULONG_MAX) return;" also is
> necessary. It will happened when unmap only go to _flush_walk, then
> enter this tlb_sync.
> ---
>   drivers/iommu/mtk_iommu.c | 29 +++++++++++++++++++++++++----
>   drivers/iommu/mtk_iommu.h |  1 +
>   2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 5f594d6..8712afc 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -234,7 +234,12 @@ static void mtk_iommu_tlb_flush_page_nosync(struct iommu_iotlb_gather *gather,
>   					    unsigned long iova, size_t granule,
>   					    void *cookie)
>   {
> -	mtk_iommu_tlb_add_flush_nosync(iova, granule, granule, true, cookie);
> +	struct mtk_iommu_data *data = cookie;
> +	struct iommu_domain *domain = &data->m4u_dom->domain;
> +
> +	data->is_in_tlb_gather_add_page = true;
> +	iommu_iotlb_gather_add_page(domain, gather, iova, granule);
> +	data->is_in_tlb_gather_add_page = false;
>   }
>   
>   static const struct iommu_flush_ops mtk_iommu_flush_ops = {
> @@ -453,12 +458,28 @@ static void mtk_iommu_flush_iotlb_all(struct iommu_domain *domain)
>   static void mtk_iommu_iotlb_sync(struct iommu_domain *domain,
>   				 struct iommu_iotlb_gather *gather)
>   {
> +	struct mtk_iommu_data *data = mtk_iommu_get_m4u_data();
>   	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
> +	bool is_in_gather = data->is_in_tlb_gather_add_page;
> +	size_t length = gather->end - gather->start;
>   	unsigned long flags;
>   
> -	spin_lock_irqsave(&dom->pgtlock, flags);
> -	mtk_iommu_tlb_sync(mtk_iommu_get_m4u_data());
> -	spin_unlock_irqrestore(&dom->pgtlock, flags);
> +	if (gather->start == ULONG_MAX)
> +		return;
> +
> +	/*
> +	 * Avoid acquire the lock when it's in gather_add_page since the lock
> +	 * has already been held.
> +	 */
> +	if (!is_in_gather)
> +		spin_lock_irqsave(&dom->pgtlock, flags);
> +
> +	mtk_iommu_tlb_add_flush_nosync(gather->start, length, gather->pgsize,
> +				       false, data);
> +	mtk_iommu_tlb_sync(data);
> +
> +	if (!is_in_gather)
> +		spin_unlock_irqrestore(&dom->pgtlock, flags);
>   }
>   
>   static phys_addr_t mtk_iommu_iova_to_phys(struct iommu_domain *domain,
> diff --git a/drivers/iommu/mtk_iommu.h b/drivers/iommu/mtk_iommu.h
> index fc0f16e..d29af1d 100644
> --- a/drivers/iommu/mtk_iommu.h
> +++ b/drivers/iommu/mtk_iommu.h
> @@ -58,6 +58,7 @@ struct mtk_iommu_data {
>   	struct iommu_group		*m4u_group;
>   	bool                            enable_4GB;
>   	bool				tlb_flush_active;
> +	bool				is_in_tlb_gather_add_page;
>   
>   	struct iommu_device		iommu;
>   	const struct mtk_iommu_plat_data *plat_data;
>