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

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Date:	Sat, 21 May 2011 16:38:24 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	Alex Williamson <alex.williamson@...hat.com>,
	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 2011-05-18 03:57, Alex Williamson wrote:
> On Tue, 2011-05-17 at 13:41 -0600, Alex Williamson wrote:
>> 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,
> 
> David, what do you think of this instead?  Thanks,
> 
> Alex
> 
> intel-iommu: Flush unmaps at domain_exit
> 
> From: Alex Williamson <alex.williamson@...hat.com>
> 
> We typically batch unmaps to be lazily flushed out at
> regular intervals.  When we destroy a domain, we need
> to force a flush of these lazy unmaps to be sure none
> reference the domain we're about to free.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
> 
>  drivers/pci/intel-iommu.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> 
> diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> index d552d2c..b04f84e 100644
> --- a/drivers/pci/intel-iommu.c
> +++ b/drivers/pci/intel-iommu.c
> @@ -1416,6 +1416,10 @@ static void domain_exit(struct dmar_domain *domain)
>  	if (!domain)
>  		return;
>  
> +	/* Flush any lazy unmaps that may reference this domain */
> +	if (!intel_iommu_strict)
> +		flush_unmaps_timeout(0);
> +
>  	domain_remove_dev_info(domain);
>  	/* destroy iovas */
>  	put_iova_domain(&domain->iovad);
> 
> 

Can we get this resolved for 2.6.39.1? Via David's patch, or Alex's
(which works for me), or whatever. It's a really annoying regression of
.39 when you want to run with IOMMU enabled.

Thanks,
Jan


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