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

[Tianyu Lan <ltykernel@xxxxxxxxx>]

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.