Commit 6275714a72 for qemu.org

commit 6275714a72b217b13032d9f076ab3fde9e9bf1c5
Author: Doug Cook (WINDOWS) <dcook@microsoft.com>
Date:   Tue Aug 18 17:58:12 2026 +0000

    target/i386/whpx: handle processor reset

    WHPX is not properly handling processor reset:

    - Does not reset partition, so several registers (e.g. Hypercall,
      GuestOsId) carry values forward as "Locked" into the next session.
    - Does not clear hypervisor-managed TSC deadline (live-lock).
    - Does not re-arm the wait-for-SIPI trigger, so all CPUs start running
      immediately after reset.

    Some firmware may tolerate this, but OVMF does not. Typical result is
    that boot hangs or ends in triple-fault, e.g.

      qemu-system-x86_64: WHPX: Unexpected VP exit code 4

    After this patch, I am able to boot to Windows desktop, reset, and boot
    back to Windows desktop. Tried many times in sequence with no problems.
    Used several different reset mechanisms (OS shutdown menu, external
    "reset", watchdog reset) with no problems.

    Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/2402
    Signed-off-by: Doug Cook <dcook@microsoft.com>
    Reviewed-by: Mohamed Mediouni <mohamed@unpredictable.fr>

    Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>

diff --git a/target/i386/whpx/whpx-all.c b/target/i386/whpx/whpx-all.c
index fd3b2acb58..366de31273 100644
--- a/target/i386/whpx/whpx-all.c
+++ b/target/i386/whpx/whpx-all.c
@@ -528,6 +528,35 @@ void whpx_set_registers(CPUState *cpu, WHPXStateLevel level)

     assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu));

+    /* Assumes that cpu_synchronize_all_post_reset() runs cpu 0 first. */
+    if (level == WHPX_LEVEL_RESET_STATE && cpu->cpu_index == 0) {
+        hr = whp_dispatch.WHvResetPartition(whpx->partition);
+        if (FAILED(hr)) {
+            error_report("WHPX: Failed to reset partition, hr=%08lx", hr);
+        }
+    }
+
+    /* Reset hypervisor-owned TSC deadline. */
+    if (level == WHPX_LEVEL_RESET_STATE) {
+        WHV_REGISTER_VALUE tsc_deadline = {};
+
+        whpx_set_reg(cpu, WHvX64RegisterTscDeadline, tsc_deadline);
+    }
+
+    /*
+     * Re-arm partition's wait-for-SIPI state.
+     * whpx_vcpu_run() ignores cpu->halted, depends on SIPI for this.
+     * This must follow WHvResetPartition.
+     */
+    if (level == WHPX_LEVEL_RESET_STATE && whpx_irqchip_in_kernel()) {
+        WHV_REGISTER_VALUE activity = {};
+
+        whpx_get_reg(cpu, WHvRegisterInternalActivityState, &activity);
+        activity.InternalActivity.StartupSuspend = !cpu_is_bsp(x86_cpu);
+        activity.InternalActivity.HaltSuspend = 0;
+        whpx_set_reg(cpu, WHvRegisterInternalActivityState, activity);
+    }
+
     /*
      * Following MSRs have side effects on the guest or are too heavy for
      * runtime. Limit them to full state update.