Re: [PATCH v5 06/10] swiotlb: Zero out bounce buffer for untrusted device

Christoph Hellwig
2019-07-25T11:49:09Z

> index 43c88626a1f3..edc84a00b9f9 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -35,6 +35,7 @@
> #include <linux/scatterlist.h>
> #include <linux/mem_encrypt.h>
> #include <linux/set_memory.h>
> +#include <linux/pci.h>
> #ifdef CONFIG_DEBUG_FS
> #include <linux/debugfs.h>
> #endif
> @@ -562,6 +563,11 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
> */
> for (i = 0; i < nslots; i++)
> io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
> +
> + /* Zero out the bounce buffer if the consumer is untrusted. */
> + if (dev_is_untrusted(hwdev))
> + memset(phys_to_virt(tlb_addr), 0, alloc_size);

Hmm. Maybe we need to move the untrusted flag to struct device?
Directly poking into the pci_dev from swiotlb is a bit of a layering
violation.

> +
> if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
> (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
> swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);

Also for the case where we bounce here we only need to zero the padding
(if there is any), so I think we could optimize this a bit.