Re: [RFC PATCH V3 09/11] HV/IOMMU: Enable swiotlb bounce buffer for Isolation VM

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:

quoted

@@ -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.