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Re: [RFC PATCH V3 09/11] HV/IOMMU: Enable swiotlb bounce buffer for Isolation VM
- To: Tianyu Lan <ltykernel@xxxxxxxxx>, kys@xxxxxxxxxxxxx, haiyangz@xxxxxxxxxxxxx, sthemmin@xxxxxxxxxxxxx, wei.liu@xxxxxxxxxx, decui@xxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx, mingo@xxxxxxxxxx, bp@xxxxxxxxx, x86@xxxxxxxxxx, hpa@xxxxxxxxx, arnd@xxxxxxxx, dave.hansen@xxxxxxxxxxxxxxx, luto@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, kirill.shutemov@xxxxxxxxxxxxxxx, rppt@xxxxxxxxxx, hannes@xxxxxxxxxxx, cai@xxxxxx, krish.sadhukhan@xxxxxxxxxx, saravanand@xxxxxx, Tianyu.Lan@xxxxxxxxxxxxx, konrad.wilk@xxxxxxxxxx, hch@xxxxxx, m.szyprowski@xxxxxxxxxxx, robin.murphy@xxxxxxx, jgross@xxxxxxxx, sstabellini@xxxxxxxxxx, joro@xxxxxxxxxx, will@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, davem@xxxxxxxxxxxxx, kuba@xxxxxxxxxx, jejb@xxxxxxxxxxxxx, martin.petersen@xxxxxxxxxx
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Wed, 2 Jun 2021 12:02:03 -0400
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- Delivery-date: Wed, 02 Jun 2021 16:03:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 6/2/21 11:01 AM, Tianyu Lan wrote:
> 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.
Right. But pci_xen_swiotlb_detect() will only do something for Xen PV guests,
and those guests don't run on hyperV. It's either xen_pv_domain() (i.e.
hypervisor_is_type(X86_HYPER_XEN_PV)) or
hypervisor_is_type(X86_HYPER_MS_HYPERV) but never both. So I don't think there
needs to be a dependency between the two callbacks.
-boris
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