From: Mathias Nyman
> Sent: 17 May 2017 16:32
> There is no reason to restrict allocations to the first 16MB ISA DMA
> addresses.
>
> It is causing problems in a virtualization setup with enabled IOMMU
> (x86_64). The result is that USB is not working in the VM.
...
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index 12b573c..1f1687e 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -56,7 +56,7 @@ static struct xhci_segment *xhci_segment_alloc(struct xhci_hcd *xhci,
> }
>
> if (max_packet) {
> - seg->bounce_buf = kzalloc(max_packet, flags | GFP_DMA);
> + seg->bounce_buf = kzalloc(max_packet, flags);
This might allocate memory that the device cannot access.
So can only work if dma_map_single() itself allocates a bounce buffer.
There must be a sane way to do this that doesn't ever require
double copies.
David