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Subject: Re: [RFC PATCH V3 09/11] HV/IOMMU: Enable swiotlb bounce buffer for
 Isolation VM
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>, kys@microsoft.com,
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References: <20210530150628.2063957-1-ltykernel@gmail.com>
 <20210530150628.2063957-10-ltykernel@gmail.com>
 <9488c114-81ad-eb67-79c0-5ed319703d3e@oracle.com>
From:   Tianyu Lan <ltykernel@gmail.com>
Message-ID: <a023ee3f-ce85-b54f-79c3-146926bf3279@gmail.com>
Date:   Wed, 2 Jun 2021 23:01:36 +0800
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Hi Boris:
	Thanks for your review.

On 6/2/2021 9:16 AM, Boris Ostrovsky wrote:
> 
> On 5/30/21 11:06 AM, Tianyu Lan wrote:
>> @@ -91,6 +92,6 @@ int pci_xen_swiotlb_init_late(void)
>>   EXPORT_SYMBOL_GPL(pci_xen_swiotlb_init_late);
>>   
>>   IOMMU_INIT_FINISH(2,
>> -		  NULL,
>> +		  hyperv_swiotlb_detect,
>>   		  pci_xen_swiotlb_init,
>>   		  NULL);
> 
> 
> Could you explain this change?

Hyper-V allocates its own swiotlb bounce buffer and the default
swiotlb buffer should not be allocated. swiotlb_init() in 
pci_swiotlb_init() is to allocate default swiotlb buffer.
To achieve this, put hyperv_swiotlb_detect() as the first entry in the 
iommu_table_entry list. The detect loop in the pci_iommu_alloc() will 
exit once hyperv_swiotlb_detect() is called in Hyper-V VM and other 
iommu_table_entry callback will not be called.