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[0/4] target/arm: Implement S2FWB

Message ID 20220505183950.2781801-1-peter.maydell@linaro.org
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Series target/arm: Implement S2FWB | expand

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Peter Maydell May 5, 2022, 6:39 p.m. UTC 
In the original Arm v8 two-stage translation, both stage 1 and stage
2 specify memory attributes (memory type, cacheability,
shareability); these are then combined to produce the overall memory
attributes for the whole stage 1+2 access.

The new FEAT_S2FWB feature allows the guest to enable a different
interpretation of the attribute bits in the stage 2 descriptors.
These bits can now be used to control details of how the stage 1 and
2 attributes should be combined (for instance they can say "always
use the stage 1 attributes" or "ignore the stage 1 attributes and
always be Device memory").

This series implements support for FEAT_S2FWB.  It starts by
postponing interpretation of the attribute bits in a stage 2
descriptor until the point where we need to combine them with the
stage 1 attributes.  It then pulls out the HCR_EL2.FWB=0 specific
code into its own function, so that the support for FWB=1 that we add
in patch 3 slots in neatly.  Finally, patch 4 turns it on for -cpu
max.

I have tested that a Linux nested-guest setup works OK (and that
the guest really is turning on HCR_EL2.FWB), but since we don't
do anything with memory attributes except return them in the
PAR_EL1 when the guest does AT instructions, you probably wouldn't
find bugs in this unless you explicitly went and wrote a bunch
of test cases that set up page tables and ran AT instructions to
check what memory attributes we report.

-- PMM

Peter Maydell (4):
  target/arm: Postpone interpretation of stage 2 descriptor attribute bits
  target/arm: Factor out FWB=0 specific part of combine_cacheattrs()
  target/arm: Implement FEAT_S2FWB
  target/arm: Enable FEAT_S2FWB for -cpu max

 docs/system/arm/emulation.rst |   1 +
 target/arm/cpu.h              |   5 +
 target/arm/internals.h        |   7 +-
 target/arm/cpu64.c            |  10 ++
 target/arm/helper.c           | 200 +++++++++++++++++++++++++++-------
 5 files changed, 182 insertions(+), 41 deletions(-)