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

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Date:	Mon, 16 May 2011 09:13:18 -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, 2011-05-09 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?
Thanks,

Alex

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