Pierrick Bouvier <pierrick.bouv...@linaro.org> writes: > 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.
Surely we can only honour and apply the new default to -cpu max? > > Peter, Alex, do you have any suggestion on this topic? > > Thanks, > Pierrick > >> r~ -- Alex Bennée Virtualisation Tech Lead @ Linaro
