Re: [PATCH v3] target/i386: Set maximum APIC ID to KVM prior to vCPU creation

[Zeng Guang <guang.zeng@intel.com>]

PING again !
This QEMU patch is to optimize max APIC ID set for current VM session 
introduced since linux v6.0. It's also compatible with previous linux 
version.

Thanks.

On 9/5/2022 9:27 AM, Zeng Guang wrote:
> Kindly PING!
>
> On 8/25/2022 10:52 AM, Zeng Guang wrote:
>> Specify maximum possible APIC ID assigned for current VM session to KVM
>> prior to the creation of vCPUs. By this setting, KVM can set up VM-scoped
>> data structure indexed by the APIC ID, e.g. Posted-Interrupt Descriptor
>> pointer table to support Intel IPI virtualization, with the most optimal
>> memory footprint.
>>
>> It can be achieved by calling KVM_ENABLE_CAP for KVM_CAP_MAX_VCPU_ID
>> capability once KVM has enabled it. Ignoring the return error if KVM
>> doesn't support this capability yet.
>>
>> Signed-off-by: Zeng Guang <guang.zeng@intel.com>
>> ---
>>    hw/i386/x86.c              | 4 ++++
>>    target/i386/kvm/kvm-stub.c | 5 +++++
>>    target/i386/kvm/kvm.c      | 5 +++++
>>    target/i386/kvm/kvm_i386.h | 1 +
>>    4 files changed, 15 insertions(+)
>>
>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
>> index 050eedc0c8..4831193c86 100644
>> --- a/hw/i386/x86.c
>> +++ b/hw/i386/x86.c
>> @@ -139,6 +139,10 @@ void x86_cpus_init(X86MachineState *x86ms, int default_cpu_version)
>>            exit(EXIT_FAILURE);
>>        }
>>    
>> +    if (kvm_enabled()) {
>> +        kvm_set_max_apic_id(x86ms->apic_id_limit);
>> +    }
>> +
>>        possible_cpus = mc->possible_cpu_arch_ids(ms);
>>        for (i = 0; i < ms->smp.cpus; i++) {
>>            x86_cpu_new(x86ms, possible_cpus->cpus[i].arch_id, &error_fatal);
>> diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c
>> index f6e7e4466e..e052f1c7b0 100644
>> --- a/target/i386/kvm/kvm-stub.c
>> +++ b/target/i386/kvm/kvm-stub.c
>> @@ -44,3 +44,8 @@ bool kvm_hyperv_expand_features(X86CPU *cpu, Error **errp)
>>    {
>>        abort();
>>    }
>> +
>> +void kvm_set_max_apic_id(uint32_t max_apic_id)
>> +{
>> +    return;
>> +}
>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
>> index f148a6d52f..af4ef1e8f0 100644
>> --- a/target/i386/kvm/kvm.c
>> +++ b/target/i386/kvm/kvm.c
>> @@ -5428,3 +5428,8 @@ void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask)
>>            mask &= ~BIT_ULL(bit);
>>        }
>>    }
>> +
>> +void kvm_set_max_apic_id(uint32_t max_apic_id)
>> +{
>> +    kvm_vm_enable_cap(kvm_state, KVM_CAP_MAX_VCPU_ID, 0, max_apic_id);
>> +}
>> diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
>> index 4124912c20..c133b32a58 100644
>> --- a/target/i386/kvm/kvm_i386.h
>> +++ b/target/i386/kvm/kvm_i386.h
>> @@ -54,4 +54,5 @@ uint64_t kvm_swizzle_msi_ext_dest_id(uint64_t address);
>>    bool kvm_enable_sgx_provisioning(KVMState *s);
>>    void kvm_request_xsave_components(X86CPU *cpu, uint64_t mask);
>>    
>> +void kvm_set_max_apic_id(uint32_t max_apic_id);
>>    #endif