In commit f7767ca30179 ("target/arm: Disable SME if SVE is disabled")
we added code that forces SME to be disabled if SVE is disabled.
This was something we did in the run-up to a release to avoid an
assertion failure in smcr_write() if the user disabled SVE on the
'max' CPU without disabling SME also.Now that we have corrected the code so that it doesn't assert in an SME-without-SVE setup, we can let users select it. This effectively reverts f7767ca30179. Note that this now means that command lines like "-cpu max,sve=off" which used to turn off SME and SVE will now give you a CPU with SME but not SVE. This is permitted by our loose "max can always give you extra stuff" rules, but may be unexpected to users. Mention this in the CPU property documentation. Reviewed-by: Richard Henderson <[email protected]> Reviewed-by: Alex Bennée <[email protected]> Signed-off-by: Peter Maydell <[email protected]> --- docs/system/arm/cpu-features.rst | 10 ++++++++-- target/arm/cpu.c | 10 ---------- 2 files changed, 8 insertions(+), 12 deletions(-) diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst index 024119449c..3db1f19401 100644 --- a/docs/system/arm/cpu-features.rst +++ b/docs/system/arm/cpu-features.rst @@ -323,12 +323,18 @@ SVE CPU Property Parsing Semantics enable SVE2). There are not generally any lower-level controls for disabling specific SVE sub-features. + 11) Disabling SVE does not automatically disable SME. If you want to + disable both you must use ``sve=off,sme=off``. In particular, + for the ``max`` CPU, ``sve=off`` alone will give you a CPU with + SME only (and which therefore still has the SVE vector registers). + Most users will want to disable both at once. + SVE CPU Property Examples ------------------------- - 1) Disable SVE:: + 1) Disable SVE and SME:: - $ qemu-system-aarch64 -M virt -cpu max,sve=off + $ qemu-system-aarch64 -M virt -cpu max,sve=off,sme=off 2) Implicitly enable all vector lengths for the ``max`` CPU type:: diff --git a/target/arm/cpu.c b/target/arm/cpu.c index 586202071d..32cd076f6e 100644 --- a/target/arm/cpu.c +++ b/target/arm/cpu.c @@ -1571,16 +1571,6 @@ void arm_cpu_finalize_features(ARMCPU *cpu, Error **errp) return; } - /* - * FEAT_SME is not architecturally dependent on FEAT_SVE (unless - * FEAT_SME_FA64 is present). However our implementation currently - * assumes it, so if the user asked for sve=off then turn off SME also. - * (KVM doesn't currently support SME at all.) - */ - if (cpu_isar_feature(aa64_sme, cpu) && !cpu_isar_feature(aa64_sve, cpu)) { - object_property_set_bool(OBJECT(cpu), "sme", false, &error_abort); - } - arm_cpu_sme_finalize(cpu, &local_err); if (local_err != NULL) { error_propagate(errp, local_err); -- 2.43.0
