[PATCH 0/4] fs/erofs: major alignment fixes

[Michael Walle]

Throughout the whole fs code, large (4k) data buffers are allocated
on the stack. While it is not nice, to allocate that large buffers on
the stack, there is a much more fundamental problem: it's not
aligned.

This will result in a huge amount of cache misaligned messages on
arm32 SoCs, e.g.:

 CACHE: Misaligned operation at range [x, y]

While this is more or less a warning, as it will only invalidate
surrounding data, DMA is more of a problem. Some DMA controllers
have address restrictions and because of that there is
ARCH_DMA_MINALIGN. Thus as a first fix, move all the data buffers
from the stack to the heap with proper alignment.

There are still some misalignment warnings. I've traced it to
fs_devread(). Most of the calls to blk_dread() will pass an aligned
buffer. But the main blk_dread() will just pass buf, which might
have previously been advanced by readlen. Not sure how that could be
fixed in an elegant way. The simplest would probably be just a
bounce buffer, which there is already one in blk_read() if
BOUNCE_BUFFERS is enabled. But I haven't managed to get that
working. And now, I'm running out of time.

Michael Walle (4):
  fs/erofs: align the malloc'ed data
  fs/erofs: allocate data buffers on heap with alignment (1/3)
  fs/erofs: allocate data buffers on heap with alignment (2/3)
  fs/erofs: allocate data buffers on heap with alignment (3/3)

 fs/erofs/data.c     | 125 +++++++++++++++++++++++++++++---------------
 fs/erofs/fs.c       |  14 ++++-
 fs/erofs/internal.h |   5 +-
 fs/erofs/namei.c    |  47 ++++++++++++-----
 fs/erofs/super.c    |  40 ++++++++++----
 fs/erofs/zmap.c     |  61 +++++++++++++++------
 6 files changed, 205 insertions(+), 87 deletions(-)

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2.47.3