Re: [PATCH 07/13] target/i386: Allow elision of kvm_enable_x2apic()

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 4/9/23 15:40, Paolo Bonzini wrote:
> On 9/4/23 14:43, Philippe Mathieu-Daudé wrote:
>> Call kvm_enabled() before kvm_enable_x2apic() to
>> let the compiler elide its call.
>>
>> Suggested-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> ---
>>   hw/i386/intel_iommu.c      | 2 +-
>>   hw/i386/x86.c              | 2 +-
>>   target/i386/kvm/kvm-stub.c | 7 -------
>>   3 files changed, 2 insertions(+), 9 deletions(-)


>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
>> index a88a126123..d2920af792 100644
>> --- a/hw/i386/x86.c
>> +++ b/hw/i386/x86.c
>> @@ -136,7 +136,7 @@ void x86_cpus_init(X86MachineState *x86ms, int 
>> default_cpu_version)
>>        * With KVM's in-kernel lapic: only if X2APIC API is enabled.
>>        */
>>       if (x86ms->apic_id_limit > 255 && !xen_enabled() &&
>> -        (!kvm_irqchip_in_kernel() || !kvm_enable_x2apic())) {
>> +        kvm_enabled() && (!kvm_irqchip_in_kernel() || 
>> !kvm_enable_x2apic())) {
> 
> This "!xen && kvm" expression can be simplified.
> 
> I am queuing the series with this squashed in:
> 
> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
> index d2920af792d..3e86cf3060f 100644
> --- a/hw/i386/x86.c
> +++ b/hw/i386/x86.c
> @@ -129,14 +129,11 @@ void x86_cpus_init(X86MachineState *x86ms, int 
> default_cpu_version)
>                                                         ms->smp.max_cpus 
> - 1) + 1;
> 
>       /*
> -     * Can we support APIC ID 255 or higher?
> -     *
> -     * Under Xen: yes.
> -     * With userspace emulated lapic: no
> -     * With KVM's in-kernel lapic: only if X2APIC API is enabled.
> +     * Can we support APIC ID 255 or higher?  With KVM, that requires
> +     * both in-kernel lapic and X2APIC userspace API.
>        */
> -    if (x86ms->apic_id_limit > 255 && !xen_enabled() &&
> -        kvm_enabled() && (!kvm_irqchip_in_kernel() || 
> !kvm_enable_x2apic())) {
> +    if (x86ms->apic_id_limit > 255 && kvm_enabled() &&
> +        (!kvm_irqchip_in_kernel() || !kvm_enable_x2apic())) {
>           error_report("current -smp configuration requires kernel "
>                        "irqchip and X2APIC API support.");
>           exit(EXIT_FAILURE);
> 
> Paolo

Thank you!