linux-kernel - Re: [PATCH v3] vfio/type1: Adopt fast IOTLB flush interface when unmap IOVAs

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Date:   Wed, 24 Jan 2018 17:00:18 +0700
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, joro@...tes.org, jroedel@...e.de
Subject: Re: [PATCH v3] vfio/type1: Adopt fast IOTLB flush interface when
 unmap IOVAs

Alex / Joerg,

On 1/24/18 5:04 AM, Alex Williamson wrote:
>> @@ -648,12 +685,40 @@ static int vfio_iommu_type1_unpin_pages(void *iommu_data,
>>   	return i > npage ? npage : (i > 0 ? i : -EINVAL);
>>   }
>>   
>> +static size_t try_unmap_unpin_fast(struct vfio_domain *domain, dma_addr_t iova,
>> +				   size_t len, phys_addr_t phys,
>> +				   struct list_head *unmapped_regions)
>> +{
>> +	struct vfio_regions *entry;
>> +	size_t unmapped;
>> +
>> +	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
>> +	if (!entry)
>> +		return -ENOMEM;
>> +
>> +	unmapped = iommu_unmap_fast(domain->domain, iova, len);
>> +	if (WARN_ON(!unmapped)) {
>> +		kfree(entry);
>> +		return -EINVAL;
>> +	}
> Not sure about the handling of this, the zero check is just a
> consistency validation.  If there's nothing mapped where we think there
> should be something mapped, we warn and throw out the whole vfio_dma.
> After this patch, such an error gets warned twice, which doesn't
> really seem to be an improvement.
> 

Since iommu_unmap() and iommu_unmap_fast() can return errors, instead of just zero check,
we should also check for errors, warn, and bail out the whole vfio_dma.

Thanks,
Suravee