linux-kernel - Re: [PATCH v4 3/7] iommu/mediatek: Use gather to achieve the tlb range flush

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Date:   Thu, 24 Oct 2019 15:22:32 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Will Deacon <will@...nel.org>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>,
        Evan Green <evgreen@...omium.org>,
        Robin Murphy <robin.murphy@....com>,
        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 v4 3/7] iommu/mediatek: Use gather to achieve the tlb
 range flush

On Wed, 2019-10-23 at 17:55 +0100, Will Deacon wrote:
> On Wed, Oct 16, 2019 at 11:33:08AM +0800, 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.
> > 
> > Suggested-by: Tomasz Figa <tfiga@...omium.org>
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> >  drivers/iommu/mtk_iommu.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index c2f6c78..81ac95f 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -245,11 +245,9 @@ static void mtk_iommu_tlb_flush_page_nosync(struct iommu_iotlb_gather *gather,
> >  					    void *cookie)
> >  {
> >  	struct mtk_iommu_data *data = cookie;
> > -	unsigned long flags;
> > +	struct iommu_domain *domain = &data->m4u_dom->domain;
> >  
> > -	spin_lock_irqsave(&data->tlb_lock, flags);
> > -	mtk_iommu_tlb_add_flush_nosync(iova, granule, granule, true, cookie);
> > -	spin_unlock_irqrestore(&data->tlb_lock, flags);
> > +	iommu_iotlb_gather_add_page(domain, gather, iova, granule);
> 
> You need to be careful here, because iommu_iotlb_gather_add_page() can
> call iommu_tlb_sync() in some situations and you don't hold the lock.

The mtk_iommu_iotlb_sync below already has the lock in it, so I delete
the lock here.

> 
> >  static const struct iommu_flush_ops mtk_iommu_flush_ops = {
> > @@ -469,9 +467,15 @@ 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();
> > +	size_t length = gather->end - gather->start;
> >  	unsigned long flags;
> >  
> > +	if (gather->start == ULONG_MAX)
> > +		return;
> > +
> >  	spin_lock_irqsave(&data->tlb_lock, flags);
> > +	mtk_iommu_tlb_add_flush_nosync(gather->start, length, gather->pgsize,
> > +				       false, data);
> >  	mtk_iommu_tlb_sync(data);
> >  	spin_unlock_irqrestore(&data->tlb_lock, flags);
> 
> Modulo my comment above, this fixes my previous comment. Given that mainline
> is already broken, I guess the runtime bisectability isn't a problem.

As the reply in [2/7]. the mainline is not broken after [2/7], it only
go to the previous status before commit(4d689b619445).

After using the iommu_gather, the iova will be the merged range in this
iotlb_sync, it is just fit to do the tlb-flush/tlb-sync. then it fixes
our potential issue(No tlb-sync for the previous tlb-flush range).

> 
> Will