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

From: Yong Wu <[email-masked]>
Date: Tue, 15 Oct 2019 13:26:06 +0800

On Mon, 2019-10-14 at 15:21 +0100, Robin Murphy wrote:
> 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.

This is more simpler! Thanks very much. I will try this.

The only concern is there is no lock in the iova_to_phys then, maybe use
the new lock instead.

> 
> Robin.
> 
> > Suggested-by: Tomasz Figa <[email-masked]>
> > Signed-off-by: Yong Wu <[email-masked]>
> > ---
> > 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;
> > 

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