[lkml]   [2020]   [Mar]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] swiotlb: Allow swiotlb to live at pre-defined address
On Thu, Mar 26, 2020 at 05:29:22PM +0100, Alexander Graf wrote:
> The swiotlb is a very convenient fallback mechanism for bounce buffering of
> DMAable data. It is usually used for the compatibility case where devices
> can only DMA to a "low region".
> However, in some scenarios this "low region" may be bound even more
> heavily. For example, there are embedded system where only an SRAM region
> is shared between device and CPU. There are also heterogeneous computing
> scenarios where only a subset of RAM is cache coherent between the
> components of the system. There are partitioning hypervisors, where
> a "control VM" that implements device emulation has limited view into a
> partition's memory for DMA capabilities due to safety concerns.
> This patch adds a command line driven mechanism to move all DMA memory into
> a predefined shared memory region which may or may not be part of the
> physical address layout of the Operating System.
> Ideally, the typical path to set this configuration would be through Device
> Tree or ACPI, but neither of the two mechanisms is standardized yet. Also,
> in the x86 MicroVM use case, we have neither ACPI nor Device Tree, but
> instead configure the system purely through kernel command line options.
> I'm sure other people will find the functionality useful going forward
> though and extend it to be triggered by DT/ACPI in the future.

I'm totally against hacking in a kernel parameter for this. We'll need
a proper documented DT or ACPI way. We also need to feed this information
into the actual DMA bounce buffering decisions and not just the swiotlb

 \ /
  Last update: 2020-03-26 18:05    [W:0.094 / U:3.524 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site