[PATCH v2 07/10] whpx: i386: add HV_X64_MSR_GUEST_IDLE when !kernel-irqchip

[Mohamed Mediouni <mohamed@unpredictable.fr>]

Add support for an oddball HV_X64_MSR_GUEST_IDLE not-quite-an-HLT
that wakes the vCPU even if EFLAGS.IF is set.

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
---
 target/i386/whpx/whpx-all.c | 46 ++++++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/target/i386/whpx/whpx-all.c b/target/i386/whpx/whpx-all.c
index 2e6679f40b..0b89fe093f 100644
--- a/target/i386/whpx/whpx-all.c
+++ b/target/i386/whpx/whpx-all.c
@@ -52,6 +52,7 @@
 /* for kernel-irqchip=off */
 #define HV_X64_MSR_APIC_FREQUENCY       0x40000023
 #define HV_X64_MSR_VP_ASSIST_PAGE       0x40000073
+#define HV_X64_MSR_GUEST_IDLE           0x400000f0
 
 static bool is_modern_os = true;
 
@@ -1543,13 +1544,16 @@ static vaddr whpx_vcpu_get_pc(CPUState *cpu, bool exit_context_valid)
     }
 }
 
-static int whpx_handle_halt(CPUState *cpu)
+static int whpx_handle_halt_generic(CPUState *cpu)
 {
+    X86CPU *x86_cpu = X86_CPU(cpu);
+    CPUX86State *env = &x86_cpu->env;
+
     int ret = 0;
 
     bql_lock();
     if (!(cpu_test_interrupt(cpu, CPU_INTERRUPT_HARD) &&
-          (cpu_env(cpu)->eflags & IF_MASK)) &&
+          ((cpu_env(cpu)->eflags & IF_MASK) || env->hflags2 & HF2_HYPERV_HLT_MASK)) &&
         !cpu_test_interrupt(cpu, CPU_INTERRUPT_NMI)) {
         cpu->exception_index = EXCP_HLT;
         cpu->halted = true;
@@ -1560,6 +1564,27 @@ static int whpx_handle_halt(CPUState *cpu)
     return ret;
 }
 
+static int whpx_handle_halt(CPUState *cpu)
+{
+    int ret = 0;
+
+    ret = whpx_handle_halt_generic(cpu);
+
+    return ret;
+}
+
+static int whpx_handle_hyperv_guestidle(CPUState *cpu)
+{
+    X86CPU *x86_cpu = X86_CPU(cpu);
+    CPUX86State *env = &x86_cpu->env;
+    int ret = 0;
+
+    env->hflags2 |= HF2_HYPERV_HLT_MASK;
+    ret = whpx_handle_halt_generic(cpu);
+
+    return ret;
+}
+
 static void whpx_vcpu_kick_out_of_hlt(CPUState *cpu) 
 {
     WHV_REGISTER_VALUE reg;
@@ -1763,9 +1788,10 @@ static void whpx_vcpu_process_async_events(CPUState *cpu)
     }
 
     if ((cpu_test_interrupt(cpu, CPU_INTERRUPT_HARD) &&
-         (env->eflags & IF_MASK)) ||
+         ((env->eflags & IF_MASK) || env->hflags2 & HF2_HYPERV_HLT_MASK)) ||
         cpu_test_interrupt(cpu, CPU_INTERRUPT_NMI)) {
         cpu->halted = false;
+        env->hflags2 &= ~HF2_HYPERV_HLT_MASK;
     }
 
     if (cpu_test_interrupt(cpu, CPU_INTERRUPT_SIPI)) {
@@ -2035,6 +2061,20 @@ int whpx_vcpu_run(CPUState *cpu)
                 }
             }
 
+            /*
+             * Windows and Linux both use this MSR.
+             * Windows 11 25H2 uses it even when not advertised.
+             */
+            if (vcpu->exit_ctx.MsrAccess.MsrNumber == HV_X64_MSR_GUEST_IDLE
+                && !vcpu->exit_ctx.MsrAccess.AccessInfo.IsWrite
+                && !whpx_irqchip_in_kernel()
+                && whpx->hyperv_enlightenments_enabled) {
+                is_known_msr = 1;
+                whpx_bump_rip(cpu, &vcpu->exit_ctx);
+                ret = whpx_handle_hyperv_guestidle(cpu);
+                break;
+            }
+
             /*
              * Linux tries to use it anyway even when not exposed. 
              * Ignore the write as the VP assist page is not used.
-- 
2.50.1 (Apple Git-155)