Subject: Re: [Resend RFC PATCH V2 10/12] HV/IOMMU: Add Hyper-V dma ops support

From: Christoph Hellwig <[email-masked]>
Date: Wed, 14 Apr 2021 17:47:29 +0200

> +static dma_addr_t hyperv_map_page(struct device *dev, struct page *page,
> +				  unsigned long offset, size_t size,
> +				  enum dma_data_direction dir,
> +				  unsigned long attrs)
> +{
> +	phys_addr_t map, phys = (page_to_pfn(page) << PAGE_SHIFT) + offset;
> +
> +	if (!hv_is_isolation_supported())
> +		return phys;
> +
> +	map = swiotlb_tbl_map_single(dev, phys, size, HV_HYP_PAGE_SIZE, dir,
> +				     attrs);
> +	if (map == (phys_addr_t)DMA_MAPPING_ERROR)
> +		return DMA_MAPPING_ERROR;
> +
> +	return map;
> +}

This largerly duplicates what dma-direct + swiotlb does.  Please use
force_dma_unencrypted to force bounce buffering and just use the generic
code.

> +	if (hv_isolation_type_snp()) {
> +		ret = hv_set_mem_host_visibility(
> +				phys_to_virt(hyperv_io_tlb_start),
> +				hyperv_io_tlb_size,
> +				VMBUS_PAGE_VISIBLE_READ_WRITE);
> +		if (ret)
> +			panic("%s: Fail to mark Hyper-v swiotlb buffer visible to host. err=%d\n",
> +			      __func__, ret);
> +
> +		hyperv_io_tlb_remap = ioremap_cache(hyperv_io_tlb_start
> +					    + ms_hyperv.shared_gpa_boundary,
> +						    hyperv_io_tlb_size);
> +		if (!hyperv_io_tlb_remap)
> +			panic("%s: Fail to remap io tlb.\n", __func__);
> +
> +		memset(hyperv_io_tlb_remap, 0x00, hyperv_io_tlb_size);
> +		swiotlb_set_bounce_remap(hyperv_io_tlb_remap);

And this really needs to go into a common hook where we currently just
call set_memory_decrypted so that all the different schemes for these
trusted VMs (we have about half a dozen now) can share code rather than
reinventing it.