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SubjectRe: [RFC PATCH V3 10/11] HV/Netvsc: Add Isolation VM support for netvsc driver
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On 6/7/2021 2:50 PM, Christoph Hellwig wrote:
> On Sun, May 30, 2021 at 11:06:27AM -0400, Tianyu Lan wrote:
>> + if (hv_isolation_type_snp()) {
>> + pfns = kcalloc(buf_size / HV_HYP_PAGE_SIZE, sizeof(unsigned long),
>> + GFP_KERNEL);
>> + for (i = 0; i < buf_size / HV_HYP_PAGE_SIZE; i++)
>> + pfns[i] = virt_to_hvpfn(net_device->recv_buf + i * HV_HYP_PAGE_SIZE) +
>> + (ms_hyperv.shared_gpa_boundary >> HV_HYP_PAGE_SHIFT);
>> +
>> + vaddr = vmap_pfn(pfns, buf_size / HV_HYP_PAGE_SIZE, PAGE_KERNEL_IO);
>> + kfree(pfns);
>> + if (!vaddr)
>> + goto cleanup;
>> + net_device->recv_original_buf = net_device->recv_buf;
>> + net_device->recv_buf = vaddr;
>> + }
>
> This probably wnats a helper to make the thing more readable. But who
> came up with this fucked up communication protocol where the host needs
> to map random pfns into a contigous range? Sometime I really have to
> wonder what crack the hyper-v people take when comparing this to the
> relatively sane approach others take.

Agree. Will add a helper function.
>
>> + for (i = 0; i < page_count; i++)
>> + dma_unmap_single(&hv_dev->device, packet->dma_range[i].dma,
>> + packet->dma_range[i].mapping_size,
>> + DMA_TO_DEVICE);
>> +
>> + kfree(packet->dma_range);
>
> Any reason this isn't simply using a struct scatterlist?

I will have a look. Thanks to reminder scatterlist.

>
>> + for (i = 0; i < page_count; i++) {
>> + char *src = phys_to_virt((pb[i].pfn << HV_HYP_PAGE_SHIFT)
>> + + pb[i].offset);
>> + u32 len = pb[i].len;
>> +
>> + dma = dma_map_single(&hv_dev->device, src, len,
>> + DMA_TO_DEVICE);
>
> dma_map_single can only be used on page baked memory, and if this is
> using page backed memory you wouldn't need to do thee phys_to_virt
> tricks. Can someone explain the mess here in more detail?

Sorry. Could you elaborate the issue? These pages in the pb array are
not allocated by DMA API and using dma_map_single() here is to map these
pages' address to bounce buffer physical address.

>
>> struct rndis_device *dev = nvdev->extension;
>> struct rndis_request *request = NULL;
>> + struct hv_device *hv_dev = ((struct net_device_context *)
>> + netdev_priv(ndev))->device_ctx;
>
> Why not use a net_device_context local variable instead of this cast
> galore?
>

OK. I will update.


Thanks.

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