lkml.org 
[lkml]   [2010]   [Jul]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management
    From
    Date
    Zach Pfeffer <zpfeffer@codeaurora.org> writes:

    > On Wed, Jul 14, 2010 at 11:05:36PM +0100, Russell King - ARM Linux wrote:
    >> On Wed, Jul 14, 2010 at 01:11:49PM -0700, Zach Pfeffer wrote:
    >> > If the DMA-API contained functions to allocate virtual space separate
    >> > from physical space and reworked how chained buffers functioned it
    >> > would probably work - but then things start to look like the VCM API
    >> > which does graph based map management.
    >>
    >> Every additional virtual mapping of a physical buffer results in
    >> additional cache aliases on aliasing caches, and more workload for
    >> developers to sort out the cache aliasing issues.
    >>
    >> What does VCM to do mitigate that?
    >
    > The VCM ensures that all mappings that map a given physical buffer:
    > IOMMU mappings, CPU mappings and one-to-one device mappings all map
    > that buffer using the same (or compatible) attributes. At this point
    > the only attribute that users can pass is CACHED. In the absence of
    > CACHED all accesses go straight through to the physical memory.
    >
    > The architecture of the VCM allows these sorts of consistency checks
    > to be made since all mappers of a given physical resource are
    > tracked. This is feasible because the physical resources we're
    > tracking are typically large.

    On x86 this is implemented in the pat code, and could reasonably be
    generalized to be cross platform.

    This is controlled by HAVE_PFNMAP_TRACKING and with entry points
    like track_pfn_vma_new.

    Given that we already have an implementation that tracks the cached
    vs non-cached attribute using the dma api. I don't see that the
    API has to change. An implementation of the cached vs non-cached
    status for arm and other architectures is probably appropriate.

    It is definitely true that getting your mapping caching attributes
    out of sync can be a problem.

    Eric



    \
     
     \ /
      Last update: 2010-07-15 03:51    [W:2.148 / U:0.108 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site