linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Support enforce_cache

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Message-ID: <07f6d0f1-0b3d-486a-a26b-483874a93b24@linux.intel.com>
Date:   Thu, 30 Nov 2023 11:48:43 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Support enforce_cache_coherency only for
 empty domains

On 2023/11/30 4:08, Jason Gunthorpe wrote:
> On Tue, Nov 14, 2023 at 09:10:33AM +0800, Lu Baolu wrote:
>> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
>> index 65d37a138c75..ce030c5b5772 100644
>> --- a/drivers/iommu/intel/iommu.h
>> +++ b/drivers/iommu/intel/iommu.h
>> @@ -602,6 +602,9 @@ struct dmar_domain {
>>   					 */
>>   	u8 dirty_tracking:1;		/* Dirty tracking is enabled */
>>   	u8 nested_parent:1;		/* Has other domains nested on it */
>> +	u8 has_mappings:1;		/* Has mappings configured through
>> +					 * iommu_map() interface.
>> +					 */
> Is it racey?
> 
> The other option is to make iommfd do this and forbid it from
> switching the enforce_cache_coherency if the IOAS has any maps
> attached. We can get the correct locking at that point.
> 
> AMD has the same issue if it ever wants to implement its per-PTE bit

Yes. It's better to do this in iommufd. With that done, we can then
remove this code.

Best regards,
baolu