On 12/8/25 14:42, Richard Henderson wrote:
On 8/12/25 17:33, Philippe Mathieu-Daudé wrote:
- if (kvm_arm_pmu_supported()) {
+ if (host_cpu_feature_supported(ARM_FEATURE_PMU, false)) {
Why is false correct here? Alternately, in the next patch, why is
it correct to pass true for the EL2 test?
I think I copied to KVM the HVF use, adapted on top of:
https://lore.kernel.org/qemu-devel/20250808070137.48716-12-
moha...@unpredictable.fr/
What is the purpose of the can_emulate parameter at all?
When using split-accel on pre-M3, we might emulate EL2:
| feat | can_emulate | retval
+ ---- + ----- + ----
> M1/M2 | ARM_FEATURE_EL2 false false> M1/M2 |
ARM_FEATURE_EL2 true true
M3/M4 | ARM_FEATURE_EL2 any true
For example in hvf.c:
static bool hvf_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
{
...
if (host_cpu_feature_supported(ARM_FEATURE_EL2, true)) {
ahcf->features |= 1ULL << ARM_FEATURE_EL2;
}
and then only when split-accel is not enabled:
hv_return_t hvf_arch_vm_create(MachineState *ms, uint32_t pa_range)
{
...
if (host_cpu_feature_supported(ARM_FEATURE_EL2, false)) {
ret = hv_vm_config_set_el2_enabled(config, true);
if (ret != HV_SUCCESS) {
goto cleanup;
}
}
What I'm looking for:
- Is this feature supported BY HW?
-> hw_init_feature
- Is this feature supported BY SW?
-> sw_init_feature
- Is this feature supported BY ANY?
-> do smth with feature
With split-accel, this isn't specific to HVF/ARM.
I can use a tri-state enum { ANY, HW, SW }.
My point, I guess, is: tcg_enabled() appears to be the only correct
setting for can_emulate, and since that's the case, it's clearer to not
have the parameter and simply test can_emulate within any subroutines.
Got it!
