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

[Paolo Bonzini]

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 <dbarb...@ventanamicro.com>
Signed-off-by: Philippe Mathieu-Daudé <phi...@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/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;