hw: i386: vapic: enable on WHPX with user-mode irqchip
Alleviate a performance bottleneck on legacy Windows guests. In my test setup, this makes Windows XP boot times be 20x faster than they're otherwise. Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr> Link: https://lore.kernel.org/r/20260226181930.53170-4-mohamed@unpredictable.fr Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Mohamed Mediouni committed
Feb 26, 2026 at 19:19 UTC
69dfc078a6f03ce643e050de6360887df6c3406c
1 file changed
+18
-6
hw/i386/vapic.c
+18
-6
@@ -16,6 +16,7 @@
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#include "system/cpus.h"
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#include "system/hw_accel.h"
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#include "system/kvm.h"
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+#include "system/whpx.h"
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#include "system/runstate.h"
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#include "system/address-spaces.h"
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#include "hw/i386/apic_internal.h"
@@ -229,7 +230,8 @@ static int evaluate_tpr_instruction(VAPICROMState *s, X86CPU *cpu,
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return -1;
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}
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- if (kvm_enabled() && !kvm_irqchip_in_kernel()) {
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+ if ((kvm_enabled() && !kvm_irqchip_in_kernel())
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+ || (whpx_enabled() && !whpx_irqchip_in_kernel())) {
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/*
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* KVM without kernel-based TPR access reporting will pass an IP that
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* points after the accessing instruction. So we need to look backward
@@ -549,7 +551,7 @@ static int patch_hypercalls(VAPICROMState *s)
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cpu_physical_memory_read(rom_paddr, rom, s->rom_size);
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for (pos = 0; pos < s->rom_size - sizeof(vmcall_pattern); pos++) {
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- if (kvm_irqchip_in_kernel()) {
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+ if (kvm_enabled() && kvm_irqchip_in_kernel()) {
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pattern = outl_pattern;
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alternates[0] = outl_pattern[7];
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alternates[1] = outl_pattern[7];
@@ -679,16 +681,25 @@ static void vapic_write(void *opaque, hwaddr addr, uint64_t data,
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}
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break;
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case 1:
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- if (kvm_enabled()) {
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+ if (kvm_enabled() || (whpx_enabled() && !whpx_irqchip_in_kernel())) {
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/*
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* Disable triggering instruction in ROM by writing a NOP.
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*
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* We cannot do this in TCG mode as the reported IP is not
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* accurate.
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+ *
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+ * Oddly enough, KVM increments EIP _before_ the execution
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+ * of the instruction is finished.
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*/
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pause_all_vcpus();
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- patch_byte(cpu, env->eip - 2, 0x66);
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- patch_byte(cpu, env->eip - 1, 0x90);
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+ if (!kvm_enabled()) {
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+ patch_byte(cpu, env->eip, 0x66);
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+ patch_byte(cpu, env->eip + 1, 0x90);
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+ }
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+ else {
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+ patch_byte(cpu, env->eip - 2, 0x66);
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+ patch_byte(cpu, env->eip - 1, 0x90);
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+ }
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resume_all_vcpus();
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}
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@@ -705,7 +716,8 @@ static void vapic_write(void *opaque, hwaddr addr, uint64_t data,
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break;
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default:
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case 4:
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- if (!kvm_irqchip_in_kernel()) {
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+ if ((kvm_enabled() && !kvm_irqchip_in_kernel())
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+ || (whpx_enabled() && !whpx_irqchip_in_kernel())) {
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apic_poll_irq(cpu->apic_state);
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}
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break;