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

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

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@xxxxxxxxxxxxxxxx>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
> ---
>   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/intel_iommu.c b/hw/i386/intel_iommu.c
> index 3ca71df369..c9961ef752 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -4053,7 +4053,7 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
>               error_setg(errp, "eim=on requires accel=kvm,kernel-irqchip=split");
>               return false;
>           }
> -        if (!kvm_enable_x2apic()) {
> +        if (kvm_enabled() && !kvm_enable_x2apic()) {
>               error_setg(errp, "eim=on requires support on the KVM side"
>                                "(X2APIC_API, first shipped in v4.7)");
>               return false;
> 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

>           error_report("current -smp configuration requires kernel "
>                        "irqchip and X2APIC API support.");
>           exit(EXIT_FAILURE);
> diff --git a/target/i386/kvm/kvm-stub.c b/target/i386/kvm/kvm-stub.c
> index f985d9a1d3..62cccebee4 100644
> --- a/target/i386/kvm/kvm-stub.c
> +++ b/target/i386/kvm/kvm-stub.c
> @@ -12,13 +12,6 @@
>   #include "qemu/osdep.h"
>   #include "kvm_i386.h"
>   
> -#ifndef __OPTIMIZE__
> -bool kvm_enable_x2apic(void)
> -{
> -    return false;
> -}
> -#endif
> -
>   bool kvm_hv_vpindex_settable(void)
>   {
>       return false;