On 12/16/24 11:50, Richard Henderson wrote:
On 12/16/24 13:26, Pierrick Bouvier wrote:
On 12/16/24 11:10, Richard Henderson wrote:
On 12/4/24 15:12, Pierrick Bouvier wrote:
qemu-system-aarch64 default pointer authentication (QARMA5) is expensive, we
spent up to 50% of the emulation time running it (when using TCG).
Switching to pauth-impdef=on is often given as a solution to speed up execution.
Thus we talked about making it the new default.
The first patch introduce a new property (pauth-qarma5) to allow to select
current default algorithm.
The second one change the default.
Pierrick Bouvier (2):
target/arm: add new property to select pauth-qarma5
target/arm: change default pauth algorithm to impdef
docs/system/arm/cpu-features.rst | 7 +++++--
docs/system/introduction.rst | 2 +-
target/arm/cpu.h | 1 +
target/arm/arm-qmp-cmds.c | 2 +-
target/arm/cpu64.c | 30 +++++++++++++++++++-----------
tests/qtest/arm-cpu-features.c | 15 +++++++++++----
6 files changed, 38 insertions(+), 19 deletions(-)
I understand the motivation, but as-is this will break migration.
I think this will need to be versioned somehow, but the only thing that really
gets
versioned are the boards, and I'm not sure how to link that to the instantiated
cpu.
From what I understood, and I may be wrong, the use case to migrate (tcg) vm
with cpu max
between QEMU versions is *not* supported, as we can't guarantee which features
are present
or not.
This doesn't affect only -cpu max, but anything using
aarch64_add_pauth_properties():
neoverse-n1, neoverse-n2, cortex-a710.
I think this is still a change worth to do, because people can get a
100% speedup with this simple change, and it's a better default than the
previous value.
In more, in case of this migration scenario, QEMU will immediately abort
upon accessing memory through a pointer.
I'm not sure about what would be the best way to make this change as
smooth as possible for QEMU users.
Peter, Alex, do you have any suggestion on this topic?
Thanks,
Pierrick
r~
