linux-kernel - Re: [PATCH] pci, dmar: flush IOTLB before exit domain

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Date:	Tue, 17 May 2011 13:41:02 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Yinghai Lu <yinghai.lu@...cle.com>, Kalle Valo <kvalo@...rom.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] pci, dmar: flush IOTLB before exit domain

On Mon, 2011-05-16 at 09:13 -0600, Alex Williamson wrote:
> On Mon, 2011-05-09 at 15:48 +0100, David Woodhouse wrote:
> > On Thu, 2011-05-05 at 18:13 -0700, Yinghai Lu wrote:
> > > @@ -3252,6 +3252,9 @@ static int device_notifier(struct notifi
> > >                 return 0;
> > >  
> > >         if (action == BUS_NOTIFY_UNBOUND_DRIVER && !iommu_pass_through) {
> > > +               /* before we remove dev with domain, flush IOTLB */
> > > +               flush_unmaps();
> > > +
> > >                 domain_remove_one_dev_info(domain, pdev);
> > >  
> > >                 if (!(domain->flags & DOMAIN_FLAG_VIRTUAL_MACHINE) && 
> > 
> > That calls flush_unmaps() without the async_umap_flush_lock held,
> > doesn't it? A few days ago I asked someone else to test this candidate
> > patch for a similar issue:
> > 
> > http://david.woodhou.se/flush-unmaps-on-unbind.patch
> 
> Copying here:
> 
> > diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> > index d552d2c..7e606d6 100644
> > --- a/drivers/pci/intel-iommu.c
> > +++ b/drivers/pci/intel-iommu.c
> > @@ -3256,8 +3259,10 @@ static int device_notifier(struct notifier_block *nb,
> >  
> >  		if (!(domain->flags & DOMAIN_FLAG_VIRTUAL_MACHINE) &&
> >  		    !(domain->flags & DOMAIN_FLAG_STATIC_IDENTITY) &&
> > -		    list_empty(&domain->devices))
> > +		    list_empty(&domain->devices)) {
> > +			flush_unmaps_timeout(0);
> >  			domain_exit(domain);
> > +		}
> >  	}
> >  
> >  	return 0;
> > @@ -3587,6 +3592,7 @@ static void intel_iommu_domain_destroy(struct iommu_domain *domain)
> >  	struct dmar_domain *dmar_domain = domain->priv;
> >  
> >  	domain->priv = NULL;
> > +	flush_unmaps_timeout(0);
> >  	vm_domain_exit(dmar_domain);
> > }
> 
> David, would it be worthwhile to push the unmaps into the
> {vm_}domain_exit() functions to avoid races like this in the future?  I
> can verify the above resolves a panic after unbinding a device from
> snd_hda_intel that I hit recently.  Do you plan to push this for .39?

BTW, is this second chunk really needed?  VM iommu mappings don't seem
to use the lazy unmap path.  Thanks,

Alex


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