linux-kernel - Re: [PATCH v2] iommu/iova: Use raw_cpu_ptr() instead of get_cpu_ptr() for ->fq

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Message-ID: <20171106084334.639512ea@t450s.home>
Date:   Mon, 6 Nov 2017 08:43:34 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org,
        vinadhy@...il.com, linux-kernel@...r.kernel.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2] iommu/iova: Use raw_cpu_ptr() instead of
 get_cpu_ptr() for ->fq

[cc +robin]

On Thu, 2 Nov 2017 18:33:50 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> On 2017-09-21 17:21:40 [+0200], Sebastian Andrzej Siewior wrote:
> > get_cpu_ptr() disabled preemption and returns the ->fq object of the
> > current CPU. raw_cpu_ptr() does the same except that it not disable
> > preemption which means the scheduler can move it to another CPU after it
> > obtained the per-CPU object.
> > In this case this is not bad because the data structure itself is
> > protected with a spin_lock. This change shouldn't matter however on RT
> > it does because the sleeping lock can't be accessed with disabled
> > preemption.  
> 
> Did this make to your tree Jörg?

Hi Sebastian,

Joerg is out on paternity leave through the end of the year, I'm
filling in in the interim.  I hadn't looked for patches this far back,
so thanks for pointing it out.  Robin, any comments?  Thanks,

Alex

> > Cc: Joerg Roedel <joro@...tes.org>
> > Cc: iommu@...ts.linux-foundation.org
> > Reported-by: vinadhy@...il.com
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > ---
> > On 2017-09-19 11:41:19 [+0200], Joerg Roedel wrote:  
> > > Hi Sebastian,  
> > Hi Jörg,
> >   
> > > I moved the flushing to driver/iommu/iova.c to share it with the Intel
> > > IOMMU and possibly other drivers too, so this patch does no longer apply
> > > to v4.14-rc1. Can you update the patch to these changes?  
> > 
> > Sure.
> > 
> > v1…v2: move the change from amd_iommu.c to iova.c
> > 
> >  drivers/iommu/iova.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> > index 33edfa794ae9..b30900025c62 100644
> > --- a/drivers/iommu/iova.c
> > +++ b/drivers/iommu/iova.c
> > @@ -570,7 +570,7 @@ void queue_iova(struct iova_domain *iovad,
> >  		unsigned long pfn, unsigned long pages,
> >  		unsigned long data)
> >  {
> > -	struct iova_fq *fq = get_cpu_ptr(iovad->fq);
> > +	struct iova_fq *fq = raw_cpu_ptr(iovad->fq);
> >  	unsigned long flags;
> >  	unsigned idx;
> >  
> > @@ -600,8 +600,6 @@ void queue_iova(struct iova_domain *iovad,
> >  	if (atomic_cmpxchg(&iovad->fq_timer_on, 0, 1) == 0)
> >  		mod_timer(&iovad->fq_timer,
> >  			  jiffies + msecs_to_jiffies(IOVA_FQ_TIMEOUT));
> > -
> > -	put_cpu_ptr(iovad->fq);
> >  }
> >  EXPORT_SYMBOL_GPL(queue_iova);
> >  
> > -- 
> > 2.14.1
> >   
> 
> Sebastian
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu

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