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

[Tianyu Lan]

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.