Re: [RFC PATCH V3 10/11] HV/Netvsc: Add Isolation VM support for netvsc driver

[Christoph Hellwig <hch@xxxxxx>]

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.

> +     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?

> +     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?

>       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?