On Wed, Jul 06, 2022 at 09:50:27PM +0200, Andrea Parri (Microsoft) wrote:
> @@ -305,6 +306,21 @@ void *dma_direct_alloc(struct device *dev, size_t size,
> ret = page_address(page);
> if (dma_set_decrypted(dev, ret, size))
> goto out_free_pages;
> +#ifdef CONFIG_HAS_IOMEM
> + /*
> + * Remap the pages in the unencrypted physical address space
> + * when dma_unencrypted_base is set (e.g., for Hyper-V AMD
> + * SEV-SNP isolated guests).
> + */
> + if (dma_unencrypted_base) {
> + phys_addr_t ret_pa = virt_to_phys(ret);
> +
> + ret_pa += dma_unencrypted_base;
> + ret = memremap(ret_pa, size, MEMREMAP_WB);
> + if (!ret)
> + goto out_encrypt_pages;
> + }
> +#endif
So:
this needs to move into dma_set_decrypted, otherwise we don't handle
the dma_alloc_pages case (never mind that this is pretty unreadable).
Which then again largely duplicates the code in swiotlb. So I think
what we need here is a low-level helper that does the
set_memory_decrypted and memremap. I'm not quite sure where it
should go, but maybe some of the people involved with memory
encryption might have good ideas. unencrypted_base should go with
it and then both swiotlb and dma-direct can call it.
> + /*
> + * If dma_unencrypted_base is set, the virtual address returned by
> + * dma_direct_alloc() is in the vmalloc address range.
> + */
> + if (!dma_unencrypted_base && is_vmalloc_addr(cpu_addr)) {
> vunmap(cpu_addr);
> } else {
> if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
> arch_dma_clear_uncached(cpu_addr, size);
> +#ifdef CONFIG_HAS_IOMEM
> + if (dma_unencrypted_base) {
> + memunmap(cpu_addr);
> + /* re-encrypt the pages using the original address */
> + cpu_addr = page_address(pfn_to_page(PHYS_PFN(
> + dma_to_phys(dev, dma_addr))));
> + }
> +#endif
> if (dma_set_encrypted(dev, cpu_addr, size))
Same on the unmap side. It might also be worth looking into reordering
the checks in some form instead o that raw dma_unencrypted_base check
before the unmap.
